# CVE-2026-3591

## Summary

- **CVE ID:** CVE-2026-3591
- **Severity:** MEDIUM
- **CVSS Score:** 5.4 (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N)
- **CWE:** CWE-562, CWE-305
- **Published:** Mar 25, 2026
- **Last Modified:** Mar 25, 2026

## Description

A use-after-return vulnerability exists in the `named` server when handling DNS queries signed with SIG(0). Using a specially-crafted DNS request, an attacker may be able to cause an ACL to improperly (mis)match an IP address. In a default-allow ACL (denying only specific IP addresses), this may lead to unauthorized access. Default-deny ACLs should fail-secure.
This issue affects BIND 9 versions 9.20.0 through 9.20.20, 9.21.0 through 9.21.19, and 9.20.9-S1 through 9.20.20-S1.
BIND 9 versions 9.18.0 through 9.18.46 and 9.18.11-S1 through 9.18.46-S1 are NOT affected.

## 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-2026-3591)
- [CNA](https://downloads.isc.org/isc/bind9/9.20.21)
- [CNA](https://downloads.isc.org/isc/bind9/9.21.20)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.36%
- **EPSS Percentile:** 29.3

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