CVE-2026-3593: Heap use-after-free vulnerability in BIND 9 DNS-over-HTTPS implementation

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-20 · updated 2026-08-24
Weakness: CWE-416

Description

A use-after-free vulnerability exists within the DNS-over-HTTPS implementation. This issue affects BIND 9 versions 9.20.0 through 9.20.22, 9.21.0 through 9.21.21, and 9.20.9-S1 through 9.20.22-S1. BIND 9 versions 9.18.0 through 9.18.48 and 9.18.11-S1 through 9.18.48-S1 are NOT affected.

Affected products

ISC BIND: from 9.20.0 before 9.20.23; from 9.21.0 before 9.21.22 — fixed in 9.20.23, 9.21.22

How to fix

Upgrade to a fixed version: ISC BIND 9.20.23, 9.21.22. Check the vendor advisory for mitigations.

References

https://downloads.isc.org/isc/bind9/9.20.23
https://downloads.isc.org/isc/bind9/9.21.22
https://kb.isc.org/docs/cve-2026-3593
https://access.redhat.com/errata/RHSA-2026:7412
https://access.redhat.com/security/cve/CVE-2026-3593
https://bugzilla.redhat.com/show_bug.cgi?id=2479770
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-3593.json

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