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

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.

Published: 2026-03-25 Last update: 2026-05-21 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-3591 is rated Low Risk (22.1/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.01%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-3591

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-03-26 — 0.01% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-3591

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.4 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 2.8 2.5 [email protected]

Weakness enumeration for CVE-2026-3591

OS Trackers for CVE-2026-3591

vendor priority summary link
alpine — CVE-2026-3591: 1 source package rows (bind); 3 state rows across 3 repos (3.22-main, 3.23-main, edge-main); fixed 3, open 0. https://security.alpinelinux.org/vuln/CVE-2026-3591
debian unimportant CVE-2026-3591 unimportant priority: Debian including 1 source packages (bind9), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2026-3591
redhat medium — https://access.redhat.com/security/cve/CVE-2026-3591
suse medium CVE-2026-3591 severity moderate: SUSE including 51 source package names (bind, bind-9.20.21-1.1, …), 161 product×package rows across 25 product lines (SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS, SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS, … (25 product lines)): Known Not Affected 141, Fixed 12, First Fixed 8. https://www.suse.com/security/cve/CVE-2026-3591/
ubuntu medium CVE-2026-3591 medium priority: Ubuntu including 3 source packages (bind9, bind9-libs, isc-dhcp), 21 status rows across 8 suites (bionic, focal, jammy, noble, questing, trusty, upstream, xenial): not-affected 10, needs-triage 7, DNE 2, released 2. https://ubuntu.com/security/CVE-2026-3591

Affected software / configurations for CVE-2026-3591

Vendor Product Version Raw CPE
isc bind >= 9.20.0, < 9.20.21 cpe:2.3:a:isc:bind:*:*:*:*:-:*:*:*
isc bind >= 9.21.0, < 9.21.20 cpe:2.3:a:isc:bind:*:*:*:*:-:*:*:*

References for CVE-2026-3591

cvelogic Threat Intelligence