Medium 5.4Published Mar 25, 2026

CVE-2026-3591A stack use-after-return flaw in SIG(0) handling code may enable ACL bypass

Updated under an hour ago (Oct 26, 2026, 7:10 AM ET)

Does this affect you?

It affects ISC BIND 9 and 1 other product. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

Do this next

Start free and add your stack

Free account, 1 product

Every CVE for ISC BIND 9

Exploited in the last 30 days

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.

CVSS: 5.4 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
Weakness (CWE): CWE-562, CWE-305
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: isc
NVD analysis: Analyzed
Record last updated: Mar 25, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

ISC BIND 9 isc:bind_9 (from the name)	from 9.20.0 through 9.20.20; from 9.21.0 through 9.21.19; from 9.20.9-S1 through 9.20.20-S1; from 9.18.0 through 9.18.46 not affected; from 9.18.11-S1 through 9.18.46-S1 not affected	CNA record
isc bind isc:bind	from 9.20.0 before 9.20.21; from 9.21.0 before 9.21.20	NVD

References

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

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.