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No exploitation reportedFix available

CVE-2021-25218

No exploitation reported by the sources we read.

  • Published2021-08-18
  • WeaknessCWE-617

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

In BIND 9.16.19, 9.17.16. Also, version 9.16.19-S1 of BIND Supported Preview Edition When a vulnerable version of named receives a query under the circumstances described above, the named process will terminate due to a failed assertion check. The vulnerability affects only BIND 9 releases 9.16.19, 9.17.16, and release 9.16.19-S1 of the BIND Supported Preview Edition.

Timeline

dates in UTC
  1. 2021-08-1819:15CVE publishedNVD

Versions per branch

NVD
Isc bind
BranchAffectedFixed in
9.16= 9.16.19no fix published
9.17= 9.17.16no fix published
Fedoraproject fedora
BranchAffectedFixed in
34.x= 34no fix published

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • bindWolfiall versions · fixed in 0
  • bindopenSUSE:Tumbleweedall versions · fixed in 9.16.20-1.4
  • bindCleanStartall versions · fixed in 9.16.20-r0
  • bindChainguardall versions · fixed in 0
  • bindAlpine:v3.24all versions · fixed in 9.16.20-r0
  • bindAlpine:v3.23all versions · fixed in 9.16.20-r0
  • bindAlpine:v3.22all versions · fixed in 9.16.20-r0
  • bindAlpine:v3.21all versions · fixed in 9.16.20-r0

10 more package ranges on OSV.dev

Vendor advisories

  • CVE-2021-25218 Red Hat Product Security

    bind: Too strict assertion check could be triggered when responses require UDP fragmentation if RRL is in use

Full record on NVD

Fix

  1. Workaround from the vendor Red Hat Product Security CVE-2021-25218 · 55 productsDisabling RRL in all views, including the builtin CHAOS class view, prevents the faulty assertion from being reached in the vulnerable versions of bind. To do that you can remove `rate-limit` from your named.conf files and provide a replacement for the builtin CHAOS view, like the one below: ``` vi…

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof of concept
Metasploit modules
none listed
Metasploit Framework

Sources

  • CNACVSS 3.17.5known since 2026-10-23
  • NVDCVSS 3.17.5read 2026-10-23
  • NVDCVSS 2.05read 2026-10-23
  • NVDweakness (CWE)CWE-617read 2026-10-23
  • FIRST EPSSEPSS score3.7 %2026-11-08
  • OSVaffected packages—
  • GitHub Advisoriesadvisory—

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published
2021-08-18
Last Modified
2026-06-17
NVD status
Modified
GitHub Advisory
GHSA-cc8x-chx9-c63q

Frequently asked questions

What is CVE-2021-25218?

In BIND 9.16.19, 9.17.16. Also, version 9.16.19-S1 of BIND Supported Preview Edition When a vulnerable version of named receives a query under the circumstances described above, the named process will terminate due to a failed assertion check. The vulnerability affects only BIND 9 releases 9.16.19, 9.17.16, and release 9.16.19-S1 of the BIND Supported Preview Edition.

Is CVE-2021-25218 actively exploited?

Active exploitation of CVE-2021-25218 has not been confirmed. Its EPSS score was 3.7% on 2026-11-08, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-25218?

CVE-2021-25218 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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