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CVE-2026-3591

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

Medium5.4EPSS 0.37%
Published
Updated
Reserved
Assigned by
isc

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.

Scores

CVSS scores of CVE-2026-3591, by who scored it
Scored byCVSSScoreVector
iscCNA (assigner)3.1Medium5.4CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
NVDNVD · Analyzed3.1Medium5.4CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
EPSS (exploitation in 30 days)
0.37% · top 69% of all CVEs (6 Nov 2026)
CISA SSVC
Exploitation: none · Automatable: no · Technical impact: partial
Loading the EPSS history…

The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.4.

Weakness

Affected products

  • ISC · BIND 9

    • affected 9.20.0 – ≤ 9.20.20
    • affected 9.21.0 – ≤ 9.21.19
    • affected 9.20.9-S1 – ≤ 9.20.20-S1
    • unaffected 9.18.0 – ≤ 9.18.46
    • unaffected 9.18.11-S1 – ≤ 9.18.46-S1

What to do

Solution: Upgrade to the patched release most closely related to your current version of BIND 9: 9.20.21, 9.21.20, or 9.20.21-S1.

Workaround: No workarounds known.

Exploitation: We are not aware of any active exploits.

References (3)

Sources

The same CVE in the primary databases and aggregators, to check against.

Badge for a README or a ticket

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Record last updated .