CVE-2026-3591 A stack use-after-return flaw in SIG(0) handling code may enable ACL bypass
A stack use-after-return in BIND's SIG(0) handling allows attackers to bypass IP-based ACLs, potentially granting unauthorized access to DNS services.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-3591?
CVE-2026-3591 is a medium-severity use after free vulnerability in Isc Bind, published on 25 Mar 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-3591?
It affects 1 product.
Products include Isc Bind.
How do I fix CVE-2026-3591?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-3591 being exploited?
There is no known exploitation of CVE-2026-3591 in the wild and no public exploit code.
Other vulnerabilities in Isc Bind
Sources
Also known as ALPINE-CVE-2026-3591, AZL-80987, BELL-CVE-2026-3591, DEBIAN-CVE-2026-3591, GHSA-5fv2-2p94-9gh7, MINI-cmfx-9wr9-2pwv and 1 more.