CVE-2026-3593 PUBLISHED

Heap use-after-free vulnerability in BIND 9 DNS-over-HTTPS implementation

Assigner: isc
Reserved: 05.03.2026 Published: 20.05.2026 Updated: 20.05.2026

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.

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:H
CVSS Score: 7.4

Attack Vector	Network	Scope	Unchanged
Attack Complexity	High	Confidentiality Impact	High
Privileges Required	None	Integrity Impact	None
User Interaction	None	Availability Impact	High

CVSS 3.1

Product Status

Vendor	ISC
Product	BIND 9
Versions	Default: unaffected affected from 9.20.0 to 9.20.22 (incl.) affected from 9.21.0 to 9.21.21 (incl.) affected from 9.20.9-S1 to 9.20.22-S1 (incl.) unaffected from 9.18.0 to 9.18.48 (incl.) unaffected from 9.18.11-S1 to 9.18.48-S1 (incl.)

Exploits

We are not aware of any active exploits.

Workarounds

Configurations not using DNS-over-HTTPS should not be affected. Disabling DNS-over-HTTPS is likewise an effective workaround.

Solutions

Upgrade to the patched release most closely related to your current version of BIND 9: 9.20.23, 9.21.22, or 9.20.23-S1.

Credits

ISC would like to thank Naresh Kandula Parmar (Nottiboy) for bringing this vulnerability to our attention.

References

Problem Types

CWE-416 Use After Free CWE

Impacts

Crafted HTTP/2 traffic sent to a DNS-over-HTTPS endpoint can be used to trigger memory corruption.