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DNSpooq DNS Vulnerabilities

Seven vulnerabilities have been discovered in the dnsmasq open-source DNS forwarder, used in a wide range of network equipment and remote access tools. These vulnerabilities could be exploited to cause DoS conditions, execute code, or spoof DNS traffic.

Threat ID:
CC-3724
Threat Severity:
Medium
Published:
20 January 2021 12:00 AM
Report a cyber attack: call 0300 303 5222 or email [email protected]

Summary

Seven vulnerabilities have been discovered in the dnsmasq open-source DNS forwarder, used in a wide range of network equipment and remote access tools. These vulnerabilities could be exploited to cause DoS conditions, execute code, or spoof DNS traffic.

Affected platforms

The following platforms are known to be affected:

dnsmasq Versions: All prior to 2.83

Threat details

Introduction

Security researchers have discovered seven vulnerabilities, collectively referred to as DNSpooq, in the dnsmasq network infrastructure software. They claim that a remote attacker could exploit some or all of these vulnerabilities to execute arbitrary code or cause a denial-of-service condition on affected systems, or perform DNS cache poisoning attacks. 

dnsmasq is a popular open-source DNS forwarder used in a wide variety of networking platforms. Most major networking vendors, as well as most popular Linux distributions, integrate dnsmasq in some way.

Known affected vendors

Below is a list of known affected vendors. Please note this list may not be comprehensive.

  • A10 networks
  • Aruba
  • Asus
  • AT&T
  • Audiocodes
  • Belden
  • Cisco
  • Comcast
  • Crosscontrol
  • D-Link
  • Dell
  • Digi international
  • General Electric
  • Google
  • Grandstream
  • Hirschmann
  • HPE
  • Huawei
  • IBM
  • Intellidesign
  • Juniper
  • Linksys
  • Motorola
  • Netgear
  • Openstack
  • Parrot
  • Peplink
  • Qualcomm
  • Raspberry
  • Red Lion Controls
  • Ruckus
  • Siemens
  • Synology
  • Technicolor
  • Teltonika
  • Ubiquiti Networks
  • Virtual Access
  • Xiaomi
  • ZTE
  • Zyxel

Vulnerability details

Four of the seven vulnerabilities appear to be the result of a fault in the DNSSEC implementation used in dnsmasq, which result in heap-based buffer overflows and potentially allow for code to be executed remotely. Two of the vulnerabilities are due to improper DNS resource name checks, which could allow a remote user to spoof DNS traffic and perform DNS cache poisoning.

Remediation advice

Affected organisations are encouraged to contact their relevant vendors and ensure any vulnerable systems are using dnsmasq 2.83 or later. A full list of affected vendors, along with their relevant updates, is available on the CERT/CC vulnerability note VU#434904.

Organisations unable to fully update should consider implementing the following partial mitigations:

  • Temporarily disable DNSSEC validation until updates are applied.
  • Configure dnsmasq to not listen to WAN interfaces if they are not required.
  • Consider implementing DNS-over-TLS (DoT) or DNS-over-HTTPS (DoH).
  • Limit maximum extension mechanisms for DNS (EDNS) message length. Please note that this disagrees with RFC5625 recommendations.
  • Limit the maximum number of queries forwarded with the --dns-forward-max= option to 150 or lower.

CVE Vulnerabilities

Status Master

CVE-2020-25681

A flaw was found in dnsmasq before version 2.83. A heap-based buffer overflow was discovered in the way RRSets are sorted before validating with DNSSEC data. An attacker on the network, who can forge DNS replies such as that they are accepted as valid, could use this flaw to cause a buffer overflow with arbitrary data in a heap memory segment, possibly executing code on the machine. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.
Status Master

CVE-2020-25682

A flaw was found in dnsmasq before 2.83. A buffer overflow vulnerability was discovered in the way dnsmasq extract names from DNS packets before validating them with DNSSEC data. An attacker on the network, who can create valid DNS replies, could use this flaw to cause an overflow with arbitrary data in a heap-allocated memory, possibly executing code on the machine. The flaw is in the rfc1035.c:extract_name() function, which writes data to the memory pointed by name assuming MAXDNAME*2 bytes are available in the buffer. However, in some code execution paths, it is possible extract_name() gets passed an offset from the base buffer, thus reducing, in practice, the number of available bytes that can be written in the buffer. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.
Status Master

CVE-2020-25683

A flaw was found in dnsmasq before version 2.83. A heap-based buffer overflow was discovered in dnsmasq when DNSSEC is enabled and before it validates the received DNS entries. A remote attacker, who can create valid DNS replies, could use this flaw to cause an overflow in a heap-allocated memory. This flaw is caused by the lack of length checks in rfc1035.c:extract_name(), which could be abused to make the code execute memcpy() with a negative size in get_rdata() and cause a crash in dnsmasq, resulting in a denial of service. The highest threat from this vulnerability is to system availability.
Status Master

CVE-2020-25684

A flaw was found in dnsmasq before version 2.83. When getting a reply from a forwarded query, dnsmasq checks in the forward.c:reply_query() if the reply destination address/port is used by the pending forwarded queries. However, it does not use the address/port to retrieve the exact forwarded query, substantially reducing the number of attempts an attacker on the network would have to perform to forge a reply and get it accepted by dnsmasq. This issue contrasts with RFC5452, which specifies a query's attributes that all must be used to match a reply. This flaw allows an attacker to perform a DNS Cache Poisoning attack. If chained with CVE-2020-25685 or CVE-2020-25686, the attack complexity of a successful attack is reduced. The highest threat from this vulnerability is to data integrity.
Status Master

CVE-2020-25685

A flaw was found in dnsmasq before version 2.83. When getting a reply from a forwarded query, dnsmasq checks in forward.c:reply_query(), which is the forwarded query that matches the reply, by only using a weak hash of the query name. Due to the weak hash (CRC32 when dnsmasq is compiled without DNSSEC, SHA-1 when it is) this flaw allows an off-path attacker to find several different domains all having the same hash, substantially reducing the number of attempts they would have to perform to forge a reply and get it accepted by dnsmasq. This is in contrast with RFC5452, which specifies that the query name is one of the attributes of a query that must be used to match a reply. This flaw could be abused to perform a DNS Cache Poisoning attack. If chained with CVE-2020-25684 the attack complexity of a successful attack is reduced. The highest threat from this vulnerability is to data integrity.
Status Master

CVE-2020-25686

A flaw was found in dnsmasq before version 2.83. When receiving a query, dnsmasq does not check for an existing pending request for the same name and forwards a new request. By default, a maximum of 150 pending queries can be sent to upstream servers, so there can be at most 150 queries for the same name. This flaw allows an off-path attacker on the network to substantially reduce the number of attempts that it would have to perform to forge a reply and have it accepted by dnsmasq. This issue is mentioned in the "Birthday Attacks" section of RFC5452. If chained with CVE-2020-25684, the attack complexity of a successful attack is reduced. The highest threat from this vulnerability is to data integrity.
Status Master

CVE-2020-25687

A flaw was found in dnsmasq before version 2.83. A heap-based buffer overflow was discovered in dnsmasq when DNSSEC is enabled and before it validates the received DNS entries. This flaw allows a remote attacker, who can create valid DNS replies, to cause an overflow in a heap-allocated memory. This flaw is caused by the lack of length checks in rfc1035.c:extract_name(), which could be abused to make the code execute memcpy() with a negative size in sort_rrset() and cause a crash in dnsmasq, resulting in a denial of service. The highest threat from this vulnerability is to system availability.

Last edited: 25 January 2021 10:24 am