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Common implementation anti-patterns related to Domain Name System (DNS) resource record (RR) processing
draft-dashevskyi-dnsrr-antipatterns-06

Document Type Active Internet-Draft (individual)
Authors Stanislav Dashevskyi , Daniel dos Santos , Jos Wetzels , Amine Amri
Last updated 2022-05-18
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draft-dashevskyi-dnsrr-antipatterns-06
Independent Submission                                     S. Dashevskyi
Internet-Draft                                             D. dos Santos
Intended status: Informational                                J. Wetzels
Expires: November 18, 2022                                       A. Amri
                                                  Forescout Technologies
                                                            May 18, 2022

            Common implementation anti-patterns related
      to Domain Name System (DNS) resource record (RR) processing
                draft-dashevskyi-dnsrr-antipatterns-06

Abstract

   This memo describes common vulnerabilities related to Domain Name
   System (DNS) response record (RR) processing as seen in several DNS
   client implementations. These vulnerabilities may lead to successful
   Denial-of-Service and Remote Code Execution attacks against the
   affected software. Where applicable, violations of RFC 1035 are
   mentioned.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 18, 2022.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
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   to this document.

Table of Contents

   1.  Introduction
   2.  Compression Pointer and Offset Validation
   3.  Label and Name Length Validation
   4.  Null-terminator Placement Validation
   5.  Response Data Length Validation
   6.  Record Count Validation
   7.  Security Considerations
   8.  IANA Considerations
   9. References
     9.1. Normative References
     9.2. Informative References
   Acknowledgements
   Authors' Addresses

1. Introduction

   Recently, there have been major vulnerabilities on DNS
   implementations that raised attention to this protocol as an
   important attack vector, such as [SIGRED], [SADDNS], and
   [DNSPOOQ] - a set of 7 critical issues affecting the DNS
   forwarder "dnsmasq".

   The authors of this memo have analyzed the DNS client implementations
   of several major TCP/IP protocol stacks and found a set of
   vulnerabilities that share common implementation flaws
   (anti-patterns). These flaws are related to processing DNS RRs
   (discussed in [RFC1035]) and may lead to critical security
   vulnerabilities.

   While implementation flaws may differ from one software project to
   another, these anti-patterns are highly likely to span across
   multiple implementations. In fact, one of the first CVEs related to
   one of the anti-patterns [CVE-2000-0333] dates back to the year 2000.
   The observations are not limited to DNS client implementations. 
   Any software that processes DNS RRs may be affected, such as 
   firewalls, intrusion detection systems, or general purpose DNS packet 
   dissectors (e.g., [CVE-2017-9345] in Wireshark). Similar issues may 
   also occur in DNS-over-HTTPS [RFC8484] and DNS-over-TLS [RFC7858]
   implementations. However, any implementation that deals with the DNS
   wire format is subject to the considerations discussed in this draft.

   [COMP-DRAFT] and [RFC5625] briefly mention some of these
   anti-patterns, but the main purpose of this memo is to provide
   technical details behind these anti-patterns, so that the common
   mistakes can be eradicated.

   We provide general recommendations on mitigating the anti-patterns.
   We also suggest that all implementations should drop
   malicious/malformed DNS replies and log them (optionally).

2. Compression Pointer and Offset Validation

   [RFC1035] defines the DNS message compression scheme that can be used
   to reduce the size of messages. When it is used, an entire domain
   name or several name labels are replaced with a (compression) pointer
   to a prior occurrence of the same name.

   The compression pointer is a combination of two octets: the two most
   significant bits are set to 1, and the remaining 14 bits are the
   OFFSET field. This field specifies the offset from the beginning of
   the DNS header, at which another domain name or label is located:

   +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
   | 1  1|                OFFSET                   |
   +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

   The message compression scheme explicitly allows a domain name to be
   represented as: (1) a sequence of unpacked labels ending with a zero
   octet; (2) a pointer; (3) a sequence of labels ending with a pointer.

   However, [RFC1035] does not explicitly state that blindly following
   compression pointers of any kind can be harmful [COMP-DRAFT], as we
   could not have had any assumptions about various implementations
   that would follow.

   Yet, any DNS packet parser that attempts to decompress domain names
   without validating the value of OFFSET is likely susceptible to
   memory corruption bugs and buffer overruns. These bugs allow for easy
   Denial-of-Service attacks, and may result in successful Remote Code
   Execution attacks.

   Pseudocode that illustrates a typical example of a broken domain name 
   parsing implementation is shown below (Snippet 1):

    1:decompress_domain_name(*name, *dns_payload) {
    2:
    3:  name_buffer[255];
    4:  copy_offset = 0;
    5:
    6:  label_len_octet = name;
    7:  dest_octet = name_buffer;
    8:
    9:  while (*label_len_octet != 0x00) {
   10:
   11:     if (is_compression_pointer(*label_len_octet)) {
   12:         ptr_offset = get_offset(label_len_octet,
                                           label_len_octet+1);
   13:         label_len_octet = dns_payload + ptr_offset + 1;
   14:     }
   15:
   16:     else {
   17:         length = *label_len_octet;
   18:         copy(dest_octet + copy_offset,
                           label_len_octet+1, *length);
   19:
   20:         copy_offset += length;
   21:         label_len_octet += length + 1;
   22:     }
   23:
   24:  }
   25:}
        Snippet 1 - A broken implementation of a function
    that is used for decompressing DNS domain names (pseudocode)

   Such implementations typically have a dedicated function for
   decompressing domain names (for example, see [CVE-2020-24338] and
   [CVE-2020-27738]). Among other parameters, these functions may
   accept a pointer to the beginning of the first name label within a
   RR ("name") and a pointer to the beginning of the DNS payload to be
   used as a starting point for the compression pointer
   ("dns_payload"). The destination buffer for the domain name
   ("name_buffer") is typically limited to 255 bytes as per
   [RFC1035] and can be allocated either in the stack or in the heap
   memory region.

   The code of the function at Snippet 1 reads the domain name
   label-by-label from a RR until it reaches the NUL octet ("0x00") that
   signifies the end of a domain name. If the current label length octet
   ("label_len_octet") is a compression pointer, the code extracts the
   value of the compression offset and uses it to "jump" to another
   label length octet. If the current label length octet is not a
   compression pointer, the label bytes will be copied into the name
   buffer, and the number of bytes copied will correspond to the value
   of the current label length octet. After the copy operation, the code
   will move on to the next label length octet.

   The first issue with this implementation is due to unchecked 
   compression offset values. The second issue is due to the absence of 
   checks that ensure that a pointer will eventually arrive at an 
   decompressed domain label. We describe these issues in more detail 
   below.

   [RFC1035] states that "... [compression pointer is] a pointer to a
   prior occurrence of the same name". Also, according to [RFC1035],
   the maximum size of DNS packets that can be sent over the UDP
   protocol is limited to 512 octets.

   The pseudocode at Snippet 1 violates these constraints, as it will
   accept a compression pointer that forces the code to read out of the
   bounds of a DNS packet. For instance, the compression pointer of
   "0xffff" will produce the offset of 16383 octets, which is most
   definitely pointing to a label length octet somewhere past the
   original DNS packet.  Supplying such offset values will most likely
   cause memory corruption issues and may lead to Denial-of-Service
   conditions (e.g., a Null pointer dereference after "label_len_octet"
   is set to an invalid address in memory). As an additional example, 
   see [CVE-2020-25767], [CVE-2020-24339], and [CVE-2020-24335].

   The pseudocode at Snippet 1 allows for jumping from a compression
   pointer to another compression pointer and it does not restrict the
   number of such jumps. That is, if a label length octet which is
   currently being parsed is a compression pointer, the code will
   perform a jump to another label, and if that other label is a
   compression pointer as well, the code will perform another jump, and
   so forth until it reaches an decompressed label. This may lead to
   unforeseen side-effects that result in security issues.

   Consider the excerpt from a DNS packet illustrated below:

           +----+----+----+----+----+----+----+----+----+----+----+----+
     +0x00 |    ID   |  FLAGS  |  QCOUNT | ANCOUNT | NSCOUNT | ARCOUNT |
           +----+----+----+----+----+----+----+----+----+----+----+----+
   ->+0x0c |0xc0|0x0c|   TYPE  |  CLASS  |0x04| t  | e  | s  | t  |0x03|
   |       +----+--|-+----+----+----+----+----+----+----+----+----+----+
   | +0x18 | c  | o| | m  |0x00|  TYPE   |  CLASS  | ................  |
   |       +----+--|-+----+----+----+----+----+----+----+----+----+----+
   |               |
   ----------------

   The packet begins with a DNS header at the offset +0x00, and its DNS
   payload contains several RRs. The first RR begins at the offset of
   12 octets (+0xc0) and its first label length octet is set to the
   value "0xc0", which indicates that it is a compression pointer. The
   compression pointer offset is computed from the two octets "0xc00c"
   and it is equal to 12. Since the broken implementation at Snippet 1
   follows this offset value blindly, the pointer will jump back to
   the first octet of the first RR (+0xc0) over and over again.  The
   code at Snippet 1 will enter an infinite loop state, since it will
   never leave the "TRUE" branch of the "while" loop.

   Apart from achieving infinite loops, the implementation flaws at
   Snippet 1 make it possible to achieve various pointer loops that have
   other effects. For instance, consider the DNS packet excerpt shown 
   below:

           +----+----+----+----+----+----+----+----+----+----+----+----+
     +0x00 |    ID   |  FLAGS  |  QCOUNT | ANCOUNT | NSCOUNT | ARCOUNT |
           +----+----+----+----+----+----+----+----+----+----+----+----+
   ->+0x0c |0x04| t  | e  | s  | t  |0xc0|0x0c| ...................... |
   |       +----+----+----+----+----+----+--|-+----+----+----+----+----+
   |                                        |
   -----------------------------------------

   With such a domain name, the implementation at Snippet 1 will first
   copy the domain label at the offset "0xc0" ("test"), then it will 
   fetch the next label length octet, which is a compression pointer 
   ("0xc0"). The compression pointer offset is computed from the two 
   octets "0xc00c" and is equal to 12 octets. The code will jump back 
   at the offset "0xc0" where the first label "test" is located. The 
   code will again copy the "test" label, and jump back to it, 
   following the compression pointer, over and over again.

   Snippet 1 does not contain any logic that restricts multiple jumps
   from the same compression pointer and does not ensure that no more
   than 255 octets are copied into the name buffer ("name_buffer"). In
   fact, the code will continue to write the label "test" into it,
   overwriting the name buffer and the stack of the heap metadata. In
   fact, attackers would have a significant degree of freedom in
   constructing shell-code, since they can create arbitrary copy chains
   with various combinations of labels and compression pointers.

   Therefore, blindly following compression pointers may not only lead
   to Denial-of-Service as pointed by [COMP-DRAFT], but also to
   successful Remote Code Execution attacks, as there may be other
   implementation issues present within the corresponding code.

   Some implementations may not follow [RFC1035], which states: "the
   first two bits [of a compression pointer octet] are ones; this allows
   a pointer to be distinguished from a label,  the label must begin
   with two zero bits because labels are restricted to 63 octets or less
   (the 10 and 01 combinations are reserved for future use)". Snippets 2
   and 3 show pseudocode that implements two functions that check
   whether a given octet is a compression pointer: correct and incorrect
   implementations respectively.

   1: unsigned char is_compression_pointer(*octet) {
   2:     if ((*octet & 0xc0) == 0xc0)
   3:         return true;
   4:     } else {
   5:         return false;
   6:     }
   7: }
          Snippet 2 - Correct compression pointer check

   1: unsigned char is_compression_pointer(*octet) {
   2:     if (*octet & 0xc0) {
   3:         return true;
   4:     } else {
   5:         return false;
   6:     }
   7: }
          Snippet 3 - Broken compression pointer check

   The correct implementation (Snippet 2) ensures that the two most
   significant bits of an octet are both set, while the broken
   implementation (Snippet 3) would consider an octet with only one of
   the two bits set as a compression pointer. This is likely an
   implementation mistake rather than an intended violation of
   [RFC1035], because there are no benefits in supporting such
   compression pointer values. The implementations related to 
   [CVE-2020-24338] and [CVE-2020-24335] had a broken 
   compression pointer check illustrated on Snippet 3.

   While incorrect implementations alone do not lead to vulnerabilities,
   they may have unforeseen side-effects when combined with other
   vulnerabilities. For instance, the first octet of the value "0x4130"
   may be incorrectly interpreted as a label length by a broken
   implementation. Such label length (65) is invalid, and is larger
   than 63 (as per [RFC1035]), and a packet that has this value should
   be discarded. However, the function shown on Snippet 3 will
   consider "0x41" to be a valid compression pointer, and the packet
   may pass the validation steps.

   This might give an additional leverage for attackers in constructing
   payloads and circumventing the existing DNS packet validation
   mechanisms.

   The first occurrence of a compression pointer in a RR (an octet with
   the 2 highest bits set to 1) must resolve to an octet within a DNS
   record with the value that is greater than 0 (i.e., it must not be a
   Null-terminator) and less than 64. The offset at which this octet is
   located must be smaller than the offset at which the compression
   pointer is located - once an implementation makes sure of that,
   compression pointer loops can never occur. 

   In small DNS implementations (e.g., embedded TCP/IP stacks) the
   support for nested compression pointers (pointers that point to a
   compressed name) should be discouraged: there is very little to be
   gained in terms of performance versus the high possibility of
   introducing errors, such as the ones discussed above.

   The code that implements domain name parsing should check the offset
   not only with respect to the bounds of a packet, but also its
   position with respect to the compression pointer in question. A
   compression pointer must not be "followed" more than once. We have 
   seen several implementations using a check that ensures that 
   a compression pointer is not followed more than several times. A 
   better alternative may be to ensure that the target of a compression
   pointer is always located before the location of the pointer in the
   packet.

3. Label and Name Length Validation

   [RFC1035] restricts the length of name labels to 63 octets, and
   lengths of domain names to 255 octets (i.e., label octets and label
   length octets). Some implementations do not explicitly enforce these
   restrictions.

   Consider the function "copy_domain_name()" shown on Snippet 4 below.
   The function is a variant of the "decompress_domain_name()" function 
   (Snippet 1), with the difference that it does not support compressed 
   labels, and copies only decompressed labels into the name buffer.

    1:copy_domain_name(*name, *dns_payload) {
    2:
    3:  name_buffer[255];
    4:  copy_offset = 0;
    5:
    6:  label_len_octet = name;
    7:  dest_octet = name_buffer;
    8:
    9:  while (*label_len_octet != 0x00) {
   10:
   11:     if (is_compression_pointer(*label_len_octet)) {
   12:         length = 2;
   13:         label_len_octet += length + 1;
   14:     }
   15:
   16:     else {
   17:         length = *label_len_octet;
   18:         copy(dest_octet + copy_offset,
                                label_len_octet+1, *length);
   19:
   20:         copy_offset += length;
   21:         label_len_octet += length + 1;
   22:     }
   23:
   24:  }
   25:}
        Snippet 4 - A broken implementation of a function
          that is used for copying non-compressed domain names 

   This implementation does not explicitly check for the value of the
   label length octet: this value can be up to 255 octets, and a single
   label can fill the name buffer. Depending on the memory layout of the
   target, how the name buffer is allocated, and the size of the
   malformed packet, it is possible to trigger various memory corruption
   issues.

   Both Snippets 1 and 4 restrict the size of the name buffer to 255
   octets, however there are no restrictions on the actual number of
   octets that will be copied into this buffer. In this particular case,
   a subsequent copy operation (if another label is present in the
   packet) will write past the name buffer, allowing to overwrite heap
   or stack metadata in a controlled manner.

   Similar examples of vulnerable implementations can be found in the 
   code relevant to [CVE-2020-25110], [CVE-2020-15795], and 
   [CVE-2020-27009].

   As a general recommendation, a domain label length octet must have
   the value of more than 0 and less than 64 ([RFC1035]). If this is
   not the case, an invalid value has been provided within the packet,
   or a value at an invalid position might be interpreted as a domain
   name length due to other errors in the packet (e.g., misplaced Null-
   terminator or invalid compression pointer). 

   The number of domain label characters must correspond to the value of
   the domain label octet. To avoid possible errors when interpreting
   the characters of a domain label, developers may consider
   recommendations for the preferred domain name syntax outlined in
   [RFC1035].

   The domain name length must not be more than 255 octets, including 
   the size of decompressed domain names. The NUL octet ("0x00") must 
   be present at the end of the domain name, and within the maximum name 
   length (255 octets).

4. Null-terminator Placement Validation

   A domain name must end with a NUL ("0x00") octet, as per [RFC1035].
   The implementations shown at Snippets 1 and 4 assume that this is the
   case for the RRs that they process, however names that do not have a
   NUL octet placed at the proper position within a RR are not
   discarded.

   This issue is closely related to the absence of label and name length
   checks. For example, the logic behind Snippets 1 and 4 will continue
   to copy octets into the name buffer, until a NUL octet is
   encountered. This octet can be placed at an arbitrary position
   within a RR, or not placed at all.

   Consider a pseudocode function shown on Snippet 5. The function
   returns the length of a domain name ("name") in octets to be used
   elsewhere (e.g., to allocate a name buffer of a certain size): for
   compressed domain names the function returns 2, for decompressed
   names it returns their true length using the "strlen(3)" function.

   1: get_name_length(*name) {
   2:
   3:     if (is_compression_pointer(name))
   4:         return 2;
   5:
   6:     name_len = strlen(name) + 1;
   7:     return name_len;
   8: }
     Snippet 5 - A broken implementation of a function that returns the 
                        length of a domain name

   "strlen(3)" is a standard C library function that returns the length
   of a given sequence of characters terminated by the NUL ("0x00")
   octet. Since this function also expects names to be explicitly
   Null-terminated, the return value "strlen(3)" may be also controlled
   by attackers. Through the value of "name_len" attackers may control
   the allocation of internal buffers, or specify the number by octets
   copied into these buffers, or other operations depending on the
   implementation specifics. 

   The absence of explicit checks for the NUL octet placement may also
   facilitate controlled memory reads and writes. An example of 
   vulnerable implementations can be found in the code relevant to
   [CVE-2020-25107], [CVE-2020-17440], [CVE-2020-24383], and 
   [CVE-2020-27736].

   As a general recommendation for mitigating such issues, developers
   should never trust user data to be Null-terminated. For example, to
   fix/mitigate the issue in the code Snippet 5, developers should use
   the function "strnlen(3)" that reads at most X characters(the second
   argument of the function), and ensure that X is not larger than the
   buffer allocated for the name.

5. Response Data Length Validation

   As stated in [RFC1035], every RR contains a variable length string of
   octets that contains the retrieved resource data (RDATA) (e.g., an IP
   address that corresponds to a domain name in question). The length of
   the RDATA field is regulated by the resource data length field
   (RDLENGTH), that is also present in an RR.

   Implementations that process RRs may not check for the validity of
   the RDLENGTH field value, when retrieving RDATA. Failing to do so may
   lead to out-of-bound read issues (similarly to the label and name
   length validation issues discussed in Section 3), whose impact may
   vary significantly depending on the implementation specifics. We have 
   observed instances of Denial-of-Service conditions and information 
   leaks.

   Therefore, the value of the data length byte in response DNS records
   (RDLENGTH) must reflect the number of bytes available in the field
   that describes the resource (RDATA). The format of RDATA must
   conform to the TYPE and CLASS fields of the RR.

   Examples of vulnerable implementations can be found in the code
   relevant to [CVE-2020-25108], [CVE-2020-24336], and [CVE-2020-27009].

6. Record Count Validation

   According to [RFC1035], the DNS header contains four two-octet
   fields that specify the amount of question records (QDCOUNT), answer
   records (ANCOUNT), authority records (NSCOUNT), and additional
   records (ARCOUNT).

    1: process_dns_records(dns_header, ...) {
           // ...
    2:     num_answers = dns_header->ancount
    3:     data_ptr = dns_header->data
    4:
    5:     while (num_answers > 0) {
    6:         name_length = get_name_length(data_ptr);
    7:         data_ptr += name_length + 1;
    8:
    9:         answer = (struct dns_answer_record *)data_ptr;
   10:
   11:         // process the answer record
   12:
   13:         --num_answers;
   14:     }
           // ...
   15: }
        Snippet 6 - A broken implementation of a RR processing function

   Snippet 6 illustrates a recurring implementation anti-pattern for a
   function that processes DNS RRs. The function "process_dns_records()"
   extracts the value of ANCOUNT ("num_answers") and the pointer to the
   DNS data payload ("data_ptr"). The function processes answer records
   in a loop decrementing the "num_answers" value after processing each
   record, until the value of "num_answers" becomes zero. For
   simplicity, we assume that there is only one domain name per answer.
   Inside the loop, the code calculates the domain name length
   "name_length", and adjusts the data payload pointer "data_ptr" by the
   offset that corresponds to "name_length + 1", so that the pointer
   lands on the first answer record. Next, the answer record is
   retrieved and processed, and the "num_answers" value is decremented.

   If the ANCOUNT number retrieved from the header
   ("dns_header->ancount") is not checked against the amount of data
   available in the packet and it is, e.g., larger than the number of
   answer records available, the data pointer "data_ptr" will read out
   of the bounds of the packet.  This may result in Denial-of-Service
   conditions.

   In this section, we used an example of processing answer records.
   However, the same logic is often reused for implementing the
   processing of other types of records: e.g., the number of Question
   (QCOUNT), Authority (NSCOUNT), and Additional (ARCOUNT) records. The
   number of these records specified must correspond to the actual data
   present within the packet. Therefore, all record count fields must
   be checked before fully parsing the contents of a packet.
   Specifically, Section 6.3 of[RFC5625] recommends that such malformed
   DNS packets should be dropped, and (optionally) logged.

   Examples of vulnerable implementations can be found in the code
   relevant to [CVE-2020-25109], [CVE-2020-24340],[CVE-2020-24334], and
   [CVE-2020-27737].

7. Security Considerations

   Security issues are discussed throughout this memo. The document
   discusses implementation flaws (anti-patterns) that affect the
   functionality of processing DNS RRs. The presence of such
   anti-patterns leads to bugs causing buffer overflows,
   read-out-of-bounds, and infinite loop issues. These issues have the
   following security impact: Information Leak, Denial-of-Service, and
   Remote Code Execution.

   The document lists general recommendation for the developers of DNS
   record parsing functionality that allow to prevent such
   implementation flaws, e.g., by rigorously checking the data received
   over the wire before processing it.

8. IANA Considerations

   This document introduces no new IANA considerations. Please see
   [RFC6895] for a complete review of the IANA considerations
   introduced by DNS.

9. References

9.1 Normative References

       [RFC1035]    
                Mockapetris, P., "Domain names - implementation and
                specification", RFC 1035, November 1987,
                <https://www.rfc-editor.org/info/rfc1035>.

       [RFC5625] 
                Bellis, R., "DNS Proxy Implementation Guidelines", RFC
                5625, August 2009,
                <https://www.rfc-editor.org/info/rfc5625>.

9.2 Informative References

        [SIGRED] 
                Common Vulnerabilities and Exposures, "CVE-2020-1350:
                A remote code execution vulnerability in Windows Domain 
                Name System servers", July 2020, <https://cve.mitre.org/
                cgi-bin/cvename.cgi?name=CVE-2020-1350>.

        [SADDNS] 
                Man, K., Qian, Z., Wang, Z., Zheng, X., Huang, Y., Duan,
                H., "DNS Cache Poisoning Attack Reloaded: Revolutions
                with Side Channels", November 2020, Proc. of ACM CCS'20,
                <https://dl.acm.org/doi/pdf/10.1145/3372297.3417280>.
                
       [DNSPOOQ]
                Kol, M., Oberman, S., "DNSpooq: Cache Poisoning and RCE
                in popular DNS Forwarder dnsmasq", January 2021, technical
                report, <https://www.jsof-tech.com/wp-content/uploads/
                2021/01/DNSpooq-Technical-WP.pdf>.

 [CVE-2000-0333] 
                Common Vulnerabilities and Exposures, "CVE-2000-0333:
                A denial-of-service vulnerability in tcpdump, Ethereal, 
                and other sniffer packages via malformed DNS packets", 
                2000, <https://cve.mitre.org/cgi-bin/cvename.cgi?name=
                CVE-2000-0333>.

[CVE-2020-24338]
                Common Vulnerabilities and Exposures, "CVE-2020-24338:
                A denial-of-service and remote code execution 
                vulnerability in the DNS domain name record 
                decompression functionality of picoTCP", December 2020,
                <https://cve.mitre.org/cgi-bin/cvename.cgi?name=
                CVE-2020-24338>

[CVE-2020-27738]
                Common Vulnerabilities and Exposures, "CVE-2020-27738:
                A denial-of-service and remote code execution 
                vulnerability DNS domain name record decompression 
                functionality of Nucleus NET", April 2021, 
                <https://cve.mitre.org/cgi-bin/cvename.cgi?name=
                CVE-2020-27738>.

[CVE-2020-25767]
                Common Vulnerabilities and Exposures, "CVE-2020-25767:
                An out-of-bounds read and denial-of-service vulnerability
                in the DNS name parsing routine of HCC Embedded 
                NicheStack", August 2021, <https://cve.mitre.org/
                cgi-bin/cvename.cgi?name=CVE-2020-25767>.

[CVE-2020-24339]
                Common Vulnerabilities and Exposures, "CVE-2020-24339:
                An out-of-bounds read and denial-of-service 
                vulnerability in the DNS domain name record 
                decompression functionality of picoTCP", December 2020,
                https://cve.mitre.org/cgi-bin/cvename.cgi?name=
                CVE-2020-24339>.

[CVE-2020-24335]
                Common Vulnerabilities and Exposures, "CVE-2020-24335:
                A memory corruption vulnerability in domain name parsing
                routines of uIP", December 2020, <https://cve.mitre.org/
                cgi-bin/cvename.cgi?name=CVE-2020-24335>.

[CVE-2020-25110]
                Common Vulnerabilities and Exposures, "CVE-2020-25110:
                A denial-of-service and remote code execution 
                vulnerability in the DNS implementation of Ethernut 
                Nut/OS", December 2020, <https://cve.mitre.org/cgi-bin/
                cvename.cgi?name=CVE-2020-25110>.

[CVE-2020-15795]
                Common Vulnerabilities and Exposures, "CVE-2020-15795:
                A denial-of-service and remote code execution 
                vulnerability DNS domain name label parsing
                functionality of Nucleus NET", April 2021, 
                <https://cve.mitre.org/cgi-bin/cvename.cgi?name=
                CVE-2020-15795>.

[CVE-2020-27009]
                Common Vulnerabilities and Exposures, "CVE-2020-27009:
                A denial-of-service and remote code execution 
                vulnerability DNS domain name record decompression 
                functionality of Nucleus NET", April 2021, 
                <https://cve.mitre.org/cgi-bin/cvename.cgi?name=
                CVE-2020-27009>.

[CVE-2020-25107]
                Common Vulnerabilities and Exposures, "CVE-2020-25107:
                A denial-of-service and remote code execution 
                vulnerability in the DNS implementation of Ethernut 
                Nut/OS", December 2020, <https://cve.mitre.org/cgi-bin/
                cvename.cgi?name=CVE-2020-25107>.

[CVE-2020-17440]
                Common Vulnerabilities and Exposures, "CVE-2020-17440
                A denial-of-service vulnerability in the DNS name 
                parsing implementation of uIP", December 2020, 
                <https://cve.mitre.org/cgi-bin/cvename.cgi?name=
                CVE-2020-17440>.

[CVE-2020-24383]
                Common Vulnerabilities and Exposures, "CVE-2020-24383:
                An information leak and denial-of-service vulnerability
                while parsing mDNS resource records in FNET", December
                2020, <https://cve.mitre.org/cgi-bin/cvename.cgi?name=
                CVE-2020-24383>.

[CVE-2020-27736]
                Common Vulnerabilities and Exposures, "CVE-2020-27736:
                An information leak and denial-of-service vulnerability
                in the DNS name parsing functionality of Nucleus NET",
                April 2021, <https://cve.mitre.org/cgi-bin/cvename.cgi?
                name=CVE-2020-27736>.

[CVE-2020-25108]
                Common Vulnerabilities and Exposures, "CVE-2020-25108:
                A denial-of-service and remote code execution 
                vulnerability in the DNS implementation of Ethernut
                Nut/OS", December 2020, <https://cve.mitre.org/cgi-bin/
                cvename.cgi?name=CVE-2020-25108>.

[CVE-2020-24336]
                Common Vulnerabilities and Exposures, "CVE-2020-24336:
                A buffer overflow vulnerability in the DNS 
                implementation of Contiki and Contiki-NG", December 
                2020, <https://cve.mitre.org/cgi-bin/cvename.cgi?name=
                CVE-2020-24336>.

[CVE-2020-25109]
                Common Vulnerabilities and Exposures, "CVE-2020-25109:
                A denial-of-service and remote code execution 
                vulnerability in the DNS implementation of Ethernut 
                Nut/OS", December 2020, <https://cve.mitre.org/cgi-bin/
                cvename.cgi?name=CVE-2020-25109>.

[CVE-2020-24340]
                Common Vulnerabilities and Exposures, "CVE-2020-24340:
                An out-of-bounds read and denial-of-service 
                vulnerability in the DNS response parsing functionality
                of picoTCP", December 2020, <https://cve.mitre.org/
                cgi-bin/cvename.cgi?name=CVE-2020-24340>.

[CVE-2020-24334]
                Common Vulnerabilities and Exposures, "CVE-2020-24334:
                An out-of-bounds read and denial-of-service 
                vulnerability in the DNS response parsing functionality
                of uIP", December 2020, <https://cve.mitre.org/cgi-bin/
                cvename.cgi?name=CVE-2020-24334>.

[CVE-2020-27737]
                Common Vulnerabilities and Exposures, "CVE-2020-27737:
                An information leak and denial-of-service vulnerability
                in the DNS response parsing functionality of Nucleus
                NET", April 2021, <https://cve.mitre.org/cgi-bin/
                cvename.cgi?name=CVE-2020-27737>.

 [CVE-2017-9345]
                Common Vulnerabilities and Exposures, "CVE-2017-9345:
                An infinite loop in the DNS dissector of Wireshark",
                2017, <https://cve.mitre.org/cgi-bin/cvename.cgi?name=
                CVE-2017-9345>.

    [COMP-DRAFT] 
                Koch, P., "A New Scheme for the Compression of
                Domain Names", Internet-Draft, draft-ietf-dnsind-local-
                compression-05, June 1999, Work in progress,
                <https://tools.ietf.org/html/draft-ietf-dnsind-local-
                compression-05>.

       [RFC6895] 
                Eastlake 3rd, D., "Domain Name System (DNS) IANA
                Considerations", RFC 6895, April 2013,
                <https://www.rfc-editor.org/info/rfc6982>.

       [RFC8484]
                Hoffman, P., McManus, P., "DNS Queries over HTTPS 
                (DoH)", RFC 8484, October 2018, 
                <https://www.rfc-editor.org/info/rfc8484>.

       [RFC7858]
                Hu, Z. et al, "Specification for DNS over Transport 
                Layer Security (TLS)", RFC 7858, May 2016, 
                <https://www.rfc-editor.org/info/rfc7858>.

Acknowledgements

   We would like to thank Shlomi Oberman, who has greatly contributed to
   the research that led to the creation of this document. 

Authors' Addresses

   Stanislav Dashevskyi
   Forescout Technologies
   John F. Kennedylaan, 2
   Eindhoven, 5612AB
   The Netherlands

   Email: stanislav.dashevskyi@forescout.com

   Daniel dos Santos
   Forescout Technologies
   John F. Kennedylaan, 2
   Eindhoven, 5612AB
   The Netherlands

   Email: daniel.dossantos@forescout.com

   Jos Wetzels
   Forescout Technologies
   John F. Kennedylaan, 2
   Eindhoven, 5612AB
   The Netherlands

   Email: jos.wetzels@forescout.com

   Amine Amri
   Forescout Technologies
   John F. Kennedylaan, 2
   Eindhoven, 5612AB
   The Netherlands

   Email: amine.amri@forescout.com