CVE-2026-81563

High

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.

SeverityHigh

CVSS7.5

Exploit probability—

ProductBIND 9

PublishedSep 16, 2026

First seenSep 16, 2026

Weakness typeCWE-401CWE-401

How to fix

Patches

Vendor advisories

kb.isc.org/docs/cve-2026-81563

Affected products

Product	Affected versions	Fixed in
ISC BIND 9	9.18.0 ≤ v ≤ 9.18.50, 9.20.0 ≤ v ≤ 9.20.27, 9.21.0 ≤ v ≤ 9.21.25, 9.18.11-S1 ≤ v ≤ 9.18.50-S1, 9.20.9-S1 ≤ v ≤ 9.20.27-S1	—

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