Keywords: vulnerabilities, vulnerability
Independent Submission S. Dashevskyi
Request for Comments: 9267 D. dos Santos
Category: Informational J. Wetzels
ISSN: 2070-1721 A. Amri
Forescout Technologies
July 2022
Common Implementation Anti-Patterns Related to Domain Name System (DNS)
Resource Record (RR) Processing
Abstract
This memo describes common vulnerabilities related to Domain Name
System (DNS) resource 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 document is not an Internet Standards Track specification; it is
published for informational purposes.
This is a contribution to the RFC Series, independently of any other
RFC stream. The RFC Editor has chosen to publish this document at
its discretion and makes no statement about its value for
implementation or deployment. Documents approved for publication by
the RFC Editor are not candidates for any level of Internet Standard;
see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9267.
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
(https://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
Major vulnerabilities in DNS implementations recently became evident
and raised attention to this protocol as an important attack vector,
as discussed in [SIGRED], [SADDNS], and [DNSPOOQ], the latter being 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 resource
records (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 multiple
implementations. In fact, one of the first "Common Vulnerabilities
and Exposures" (CVE) documents 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.,
the DNS dissector in Wireshark; see [CVE-2017-9345]). 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
document.
[DNS-COMPRESSION] 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 (optionally) log them.
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 one of the following: (1) a sequence of unpacked
labels ending with a zero octet, (2) a pointer, or (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 [DNS-COMPRESSION], 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 make it
easier to perform 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 (Figure 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: }
Figure 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 an
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 in Figure 1 reads the domain name label by
label from an 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 a
decompressed domain label. We describe these issues in more detail
below.
[RFC1035] states that a compression pointer is "a pointer to a prior
occurance [sic] of the same name." Also, according to [RFC1035], the
maximum size of DNS packets that can be sent over UDP is limited to
512 octets.
The pseudocode in Figure 1 violates these constraints, as it will
accept a compression pointer that forces the code to read outside the
bounds of a DNS packet. For instance, a compression pointer set to
"0xffff" will produce an offset of 16383 octets, which is most
definitely pointing to a label length octet somewhere past the bounds
of 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). For
additional examples, see [CVE-2020-25767], [CVE-2020-24339], and
[CVE-2020-24335].
The pseudocode in Figure 1 allows jumping from a compression pointer
to another compression pointer and does not restrict the number of
such jumps. That is, if a label length octet that 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 a decompressed label. This may lead to unforeseen side
effects that result in security issues.
Consider the DNS packet excerpt illustrated below:
+----+----+----+----+----+----+----+----+----+----+----+----+
+0x00 | ID | FLAGS | QDCOUNT | 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 offset +0x00, and its DNS
payload contains several RRs. The first RR begins at an offset of 12
octets (+0x0c); 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 is equal to 12. Since the broken implementation in Figure 1
follows this offset value blindly, the pointer will jump back to the
first octet of the first RR (+0x0c) over and over again. The code in
Figure 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 in
Figure 1 make it possible to achieve various pointer loops that have
other undesirable effects. For instance, consider the DNS packet
excerpt shown below:
+----+----+----+----+----+----+----+----+----+----+----+----+
+0x00 | ID | FLAGS | QDCOUNT | ANCOUNT | NSCOUNT | ARCOUNT |
+----+----+----+----+----+----+----+----+----+----+----+----+
->+0x0c |0x04| t | e | s | t |0xc0|0x0c| ...................... |
| +----+----+----+----+----+----+--|-+----+----+----+----+----+
| |
------------------------------------------
With such a domain name, the implementation in Figure 1 will first
copy the domain label at offset "0xc0" ("test"); it will then fetch
the next label length octet, which happens to be 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 to offset "0xc0" where the first label "test" is located.
The code will again copy the "test" label and then jump back to it,
following the compression pointer, over and over again.
Figure 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.
* 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 lead not only
to Denial-of-Service conditions, as pointed out by [DNS-COMPRESSION],
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 are ones. This allows a pointer to be
| distinguished from a label, since 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.)
Figures 2 and 3 show pseudocode that implements two functions that
check whether a given octet is a compression pointer; Figure 2 shows
a correct implementation, and Figure 3 shows an incorrect (broken)
implementation.
1: unsigned char is_compression_pointer(*octet) {
2: if ((*octet & 0xc0) == 0xc0)
3: return true;
4: } else {
5: return false;
6: }
7: }
Figure 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: }
Figure 3: Broken Compression Pointer Check
The correct implementation (Figure 2) ensures that the two most
significant bits of an octet are both set, while the broken
implementation (Figure 3) would consider an octet with only one of
the two bits set to be 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, similar to the code shown in Figure 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 a label length (65) is invalid and is larger
than 63 (as per [RFC1035]); a packet that has this value should be
discarded. However, the function shown in Figure 3 will consider
"0x41" to be a valid compression pointer, and the packet may pass the
validation steps.
This might give attackers additional leverage for constructing
payloads and circumventing the existing DNS packet validation
mechanisms.
The first occurrence of a compression pointer in an RR (an octet with
the two highest bits set to 1) must resolve to an octet within a DNS
record with a 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), 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 probability of introducing
errors such as those discussed above.
The code that implements domain name parsing should check the offset
with respect to not only 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 in Figure 4 below.
The function is a variant of the "decompress_domain_name()" function
(Figure 1), with the difference that it does not support compressed
labels and only copies 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: }
Figure 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 Figures 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 heap or stack
metadata to be overwritten 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 a
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 must be 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 in Figures 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 an RR are not
discarded.
This issue is closely related to the absence of label and name length
checks. For example, the logic behind Figures 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 an RR or not
placed at all.
Consider the pseudocode function shown in Figure 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: }
Figure 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 also be 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 they may perform other operations,
depending on the implementation specifics.
The absence of explicit checks for placement of the NUL octet 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 shown in the code in Figure 5, developers
should use the function "strnlen(3)", which 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), which 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, 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).
Figure 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.
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: }
Figure 6: A Broken Implementation of a Function That Processes RRs
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, for example, larger than the
number of answer records available, the data pointer ("data_ptr")
will read outside 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
(QDCOUNT), authority (NSCOUNT), and additional (ARCOUNT) records.
The specified numbers of these records 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; it discusses
implementation flaws (anti-patterns) that affect the functionality of
processing DNS RRs. The presence of such anti-patterns leads to bugs
that cause buffer overflows, read-out-of-bounds, and infinite-loop
issues. These issues have the following security impacts:
information leaks, Denial-of-Service attacks, and Remote Code
Execution attacks.
This document lists general recommendations for the developers of DNS
record parsing functionality that allow those developers to prevent
such implementation flaws, e.g., by rigorously checking the data
received over the wire before processing it.
8. IANA Considerations
This document has no IANA actions. 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", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC5625] Bellis, R., "DNS Proxy Implementation Guidelines",
BCP 152, RFC 5625, DOI 10.17487/RFC5625, August 2009,
<https://www.rfc-editor.org/info/rfc5625>.
9.2. Informative References
[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-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>.
[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", 2021, <https://cve.mitre.org/cgi-bin/
cvename.cgi?name=CVE-2020-15795>.
[CVE-2020-17440]
Common Vulnerabilities and Exposures, "CVE-2020-17440 A
denial-of-service vulnerability in the DNS name parsing
implementation of uIP", 2020, <https://cve.mitre.org/cgi-
bin/cvename.cgi?name=CVE-2020-17440>.
[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", 2020,
<https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-
2020-24334>.
[CVE-2020-24335]
Common Vulnerabilities and Exposures, "CVE-2020-24335: A
memory corruption vulnerability in domain name parsing
routines of uIP", 2020, <https://cve.mitre.org/cgi-bin/
cvename.cgi?name=CVE-2020-24335>.
[CVE-2020-24336]
Common Vulnerabilities and Exposures, "CVE-2020-24336: A
buffer overflow vulnerability in the DNS implementation of
Contiki and Contiki-NG", 2020, <https://cve.mitre.org/cgi-
bin/cvename.cgi?name=CVE-2020-24336>.
[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", 2020, <https://cve.mitre.org/cgi-bin/
cvename.cgi?name=CVE-2020-24338>.
[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", 2020, <https://cve.mitre.org/cgi-bin/
cvename.cgi?name=CVE-2020-24339>.
[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", 2020,
<https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-
2020-24340>.
[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", 2020,
<https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-
2020-24383>.
[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", 2020,
<https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-
2020-25107>.
[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", 2020,
<https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-
2020-25108>.
[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", 2020,
<https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-
2020-25109>.
[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", 2020,
<https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-
2020-25110>.
[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",
2021, <https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-
2020-25767>.
[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", 2021, <https://cve.mitre.org/cgi-bin/
cvename.cgi?name=CVE-2020-27009>.
[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", 2021,
<https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-
2020-27736>.
[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",
2021, <https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-
2020-27737>.
[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", 2021, <https://cve.mitre.org/cgi-bin/
cvename.cgi?name=CVE-2020-27738>.
[DNS-COMPRESSION]
Koch, P., "A New Scheme for the Compression of Domain
Names", Work in Progress, Internet-Draft, draft-ietf-
dnsind-local-compression-05, 30 June 1999,
<https://datatracker.ietf.org/doc/html/draft-ietf-dnsind-
local-compression-05>.
[DNSPOOQ] Kol, M. and S. Oberman, "DNSpooq: Cache Poisoning and RCE
in Popular DNS Forwarder dnsmasq", JSOF Technical Report,
January 2021, <https://www.jsof-tech.com/wp-
content/uploads/2021/01/DNSpooq-Technical-WP.pdf>.
[RFC6895] Eastlake 3rd, D., "Domain Name System (DNS) IANA
Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895,
April 2013, <https://www.rfc-editor.org/info/rfc6895>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>.
[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/info/rfc8484>.
[SADDNS] Man, K., Qian, Z., Wang, Z., Zheng, X., Huang, Y., and H.
Duan, "DNS Cache Poisoning Attack Reloaded: Revolutions
with Side Channels", Proc. 2020 ACM SIGSAC Conference on
Computer and Communications Security, CCS '20,
DOI 10.1145/3372297.3417280, November 2020,
<https://dl.acm.org/doi/pdf/10.1145/3372297.3417280>.
[SIGRED] Common Vulnerabilities and Exposures, "CVE-2020-1350: A
remote code execution vulnerability in Windows Domain Name
System servers", 2020, <https://cve.mitre.org/cgi-bin/
cvename.cgi?name=CVE-2020-1350>.
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
5612AB Eindhoven
Netherlands
Email: stanislav.dashevskyi@forescout.com
Daniel dos Santos
Forescout Technologies
John F. Kennedylaan, 2
5612AB Eindhoven
Netherlands
Email: daniel.dossantos@forescout.com
Jos Wetzels
Forescout Technologies
John F. Kennedylaan, 2
5612AB Eindhoven
Netherlands
Email: jos.wetzels@forescout.com
Amine Amri
Forescout Technologies
John F. Kennedylaan, 2
5612AB Eindhoven
Netherlands
Email: amine.amri@forescout.com