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CVE-2026-3591

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

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.

Timeline

  1. ID reserved

    By isc

  2. · 20 days later

    Published

Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.

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)
0.38% · top 68% of all CVEs (12 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.

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

References3

Sources

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

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Record last updated .