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Fencer Intel
high 7.5

CVE-2021-25218 json

A too-strict assertion check could be triggered when responses in BIND 9.16.19 and 9.17.16 require UDP fragmentation if RRL is in use

published 2021-08-18 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-12129

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
3.7%
EPSS 3.7% chance of exploitation in 30 days, percentile 89%
public exploits
0
none known

Summary

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.

Patch / fix

  • bind openSUSE Tumbleweed 9.16.20-1.4

opensuse advisories openSUSE-SU-2024:10650-1

  • bind Alpine 3.24, Alpine 3.23, Alpine 3.22 +11 more 9.16.20-r0

alpine advisories ALPINE-CVE-2021-25218

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • bind Arch Linux 9.16.20-1

arch linux advisories AVG-2303

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-25218 updated cvss 7.5

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

  • Red Hat Enterprise Linux 6 bind, bind-sdb, bind-libs, bind-utils, bind-chroot Red Hat Enterprise Linux 7 bind, bind-sdb, bind-libs, bind-utils, bind-chroot, bind-pkcs11, +6 more Red Hat Enterprise Linux 8 bind, bind-sdb, bind-libs, bind-utils, bind-chroot, bind-pkcs11, +7 more Red Hat Enterprise Linux 9 bind, bind-libs, bind-utils, bind-chroot, bind-license, python3-bind, +1 more Red Hat Virtualization 4 redhat-virtualization-host-image-update
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

3.66% chance of exploitation in the next 30 days, higher than 89% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • kb.isc.org https://kb.isc.org/v1/docs/cve-2021-25218 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:N/A:P

Affected products

  • ISC BIND9

Classification

Weakness

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.