CVE-2026-81563

SVCB AliasMode additional-data error leaks qpcache references

State: Published
Severity: 7.5 High
Published: Sep 16, 2026
Updated: Sep 17, 2026
Reserved: Aug 27, 2026

Description

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.

Scores

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

Weaknesses

CWE-401 Missing Release of Memory after Effective Lifetime

Affected Products

Product	Versions
BIND 9ISC	9.18.0 through 9.18.50Affected 9.20.0 through 9.20.27Affected 9.21.0 through 9.21.25Affected 9.18.11-S1 through 9.18.50-S1Affected 9.20.9-S1 through 9.20.27-S1Affected

References

CVE-2026-81563vendor-advisory
https://downloads.isc.org/isc/bind9/9.20.29patch
https://downloads.isc.org/isc/bind9/9.21.26patch

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