Vulnerability Report

CVE-2026-3591

Title: Use-after-return in BIND 9 named server (ACL bypass)

Auth Bypass

Proof Of Concept

No public PoC currently indexed for CVE-2026-3591.

CWE Category CWE-305

Published Date Mar 25, 2026

Modified Date May 21, 2026

Exploit Status Not Found

Score 5.4 CVSS v3.1

Exploit Probability (EPSS)

0.03%

Vulnerability Summary

CVE-2026-3591: 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.

Impacted Vendors

isc 1

Reference Links

https://downloads.isc.org/isc/bind9/9.20.21 https://downloads.isc.org/isc/bind9/9.21.20 https://kb.isc.org/docs/cve-2026-3591

CVSS v3.1

Source Entity [email protected]

Severity MEDIUM

5.4

Attack Vector

NETWORK

Complexity

LOW

Privileges

N/A

Interaction

NONE

Confidentiality

N/A

Integrity

N/A

Availability

N/A

Scope

UNCHANGED

RAW VECTOR CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

Associated Attack Patterns (CAPEC)

Total: Patterns

CVE-2026-3591 Exploits & PoCs (Proof Of Concept)

No public PoCs found in our database for this CVE.

May 21, 2026 MODIFIED

Vulnerability data updated via NVD.

March 25, 2026 MODIFIED

Vulnerability data updated via NVD.

March 25, 2026 MODIFIED

Vulnerability data updated via NVD.

March 25, 2026 MODIFIED

Vulnerability data updated via NVD.

Attack Vector Matrix

Access Vector NETWORK

Complexity LOW

Privileges N/A

Interaction NONE

CVSS Vector String


                                    CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

Affected Stack

No specific products linked.