CVE-2021-45957: Dnsmasq 2.86 has a heap-based buffer overflow in answer_request (called from FuzzAnswerTheRequest and fuzz_rfc

This week

CRITICAL 9.8REMOTEDOWNGRADE

CVE-2021-45957 is a critical-severity flaw (CVSS 9.8) affecting dnsmasq. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Dnsmasq 2.86 has a heap-based buffer overflow in answer_request (called from FuzzAnswerTheRequest and fuzz_rfc1035.c). NOTE: the vendor's position is that CVE-2021-45951 through CVE-2021-45957 "do not represent real vulnerabilities, to the best of our knowledge.

Why this priority

Critical severity
Public exploit reference
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	2.6% (top 15%)
CISA exploited list	No
Weakness	CWE-787
Published	2022-01-01
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: thekelleys

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2022-01-01 00:15 UTCPublished CVE record published
2026-06-17 04:14 UTCUpdated Record last modified

thekelleys dnsmasq DOWNGRADE

Affected: 2.86

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.86

1. Check installed version

apt-cache policy dnsmasq || rpm -q dnsmasq || dnsmasq --version

2. No fixed release: DOWNGRADE to a release before 2.86 (Debian / Ubuntu)

apt-cache madison dnsmasq sudo apt install dnsmasq=<VERSION_BEFORE_2.86> sudo apt-mark hold dnsmasq

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list dnsmasq sudo dnf downgrade dnsmasq-<VERSION_BEFORE_2.86> sudo dnf versionlock add dnsmasq

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-45957?

dnsmasq: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-45957 being exploited?

CVE-2021-45957 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-45957 affect?

CVE-2021-45957 affects dnsmasq. Severity is critical (CVSS 9.8). Dnsmasq 2.86 has a heap-based buffer overflow in answer_request (called from FuzzAnswerTheRequest and fuzz_rfc1035.c). NOTE: the vendor's position is that CVE-2021-45951 through CVE-2021-45957 "do not represent real vulnerabilities, to the

How urgent is CVE-2021-45957?

Priority 66/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

Software pages

Dnsmasq vulnerabilities

Related CVEs

CVE-2026-12725 MEDIUM 5.9 UPGRADE MITIGATE A heap-based buffer overflow was found in dnsmasq
CVE-2026-12969 MEDIUM 5.3 MITIGATE UPGRADE An out-of-bounds read vulnerability exists in dnsmasq's find_soa() function in src/rfc1035.c
CVE-2023-49441 HIGH 7.5 DOWNGRADE dnsmasq 2.9 is vulnerable to Integer Overflow via forward_query.
CVE-2023-28450 HIGH 7.5 UPGRADE An issue was discovered in Dnsmasq before 2.90
CVE-2022-0934 HIGH 7.5 UPGRADE MITIGATE A single-byte, non-arbitrary write/use-after-free flaw was found in dnsmasq

References

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