CVE-2026-81563 PUBLISHED

SVCB AliasMode additional-data error leaks qpcache references

Assigner: isc
Reserved: 27.08.2026 Published: 16.09.2026 Updated: 16.09.2026

A BIND resolver encountering an SVCB/HTTPS AliasMode record referencing 14 or more SVCB/HTTPS ServiceMode records may fail to properly deallocate internal resources. If this happens repeatedly, resource exhaustion will eventually prevent the resolver from performing new recursive lookups. This issue affects BIND 9 versions 9.18.0 through 9.18.50, 9.20.0 through 9.20.27, 9.21.0 through 9.21.25, 9.18.11-S1 through 9.18.50-S1, and 9.20.9-S1 through 9.20.27-S1.

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS Score: 7.5

Attack Vector	Network	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	None
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 9.18.0 to 9.18.50 (incl.) affected from 9.20.0 to 9.20.27 (incl.) affected from 9.21.0 to 9.21.25 (incl.) affected from 9.18.11-S1 to 9.18.50-S1 (incl.) affected from 9.20.9-S1 to 9.20.27-S1 (incl.)

Exploits

We are not aware of any active exploits.

Workarounds

No workarounds known.

Solutions

Upgrade to the patched release most closely related to your current version of BIND 9: 9.20.29, 9.21.26, or 9.20.29-S1.

Credits

ISC would like to thank Samy Medjahed/Ap4sh for bringing this vulnerability to our attention.

References

Problem Types

CWE-401 Missing Release of Memory after Effective Lifetime CWE

Impacts

Repeated successful attacks can result in memory use beyond configured limits until the system memory is exhausted or `named` is terminated by the operating system. Either case results in a denial-of-service attack.