# CVE-2025-40777

## Summary

- **CVE ID:** CVE-2025-40777
- **Severity:** HIGH
- **CVSS Score:** 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)
- **CWE:** CWE-617
- **Published:** Jul 16, 2025
- **Last Modified:** Mar 12, 2026

## Description

If a `named` caching resolver is configured with `serve-stale-enable` `yes`, and with `stale-answer-client-timeout` set to `0` (the only allowable value other than `disabled`), and if the resolver, in the process of resolving a query, encounters a CNAME chain involving a specific combination of cached or authoritative records, the daemon will abort with an assertion failure.
This issue affects BIND 9 versions 9.20.0 through 9.20.10, 9.21.0 through 9.21.9, and 9.20.9-S1 through 9.20.10-S1.

## Affected Products

- ISC — BIND 9 (9.20.0)
- ISC — BIND 9 (9.21.0)
- ISC — BIND 9 (9.20.9-S1)
- ISC — BIND 9 (9.18.0)
- ISC — BIND 9 (9.18.11-S1)

## References

- [CNA](https://kb.isc.org/docs/cve-2025-40777)
- [CVE](http://www.openwall.com/lists/oss-security/2025/07/16/6)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.92%
- **EPSS Percentile:** 58.2

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._