CVE-2026-3591Network attack vector

Authenticated ACL bypass via SIG(0) use-after-return

Published Mar 25, 2026 · Updated Mar 25, 2026

Authentication bypass in ISC BIND 9 allows remote authenticated users to bypass IP-based ACL restrictions with a crafted SIG(0)-signed DNS query. The named server reads stale stack data during ACL matching after SIG(0) processing retains an address beyond its owning function's return. Default-allow ACLs are exposed to unauthorized access; default-deny ACLs fail secure in affected 9.20, 9.21, and 9.20-S releases.

CVSS severity5.4
Medium
EPSS probability0.36%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in ISC BIND 9 allows remote authenticated users to bypass IP-based ACL restrictions with a crafted SIG(0)-signed DNS query. The named server reads stale stack data during ACL matching after SIG(0) processing retains an address beyond its owning function's return. Default-allow ACLs are exposed to unauthorized access; default-deny ACLs fail secure in affected 9.20, 9.21, and 9.20-S releases.

The record

CVE
CVE-2026-3591
Published
Mar 25, 2026
Updated
Mar 25, 2026
Vendor
Internet Systems Consortium
Product
BIND 9
Classifications
CWE-562, CWE-305, T1190
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 25, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 25, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=9.20.0 <=9.20.20
  2. Affected versionversion=9.20.9-S1 <=9.20.20-S1
  3. Affected versionversion=9.21.0 <=9.21.19

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Internet Systems Consortium · BIND 9version=9.20.0 <=9.20.20; version=9.20.9-S1 <=9.20.20-S1; version=9.21.0 <=9.21.19

Published CVSS scores

5.4Internet Systems ConsortiumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-562Return of Stack Variable Address
CWE-305Authentication Bypass by Primary Weakness
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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