---
id: CVE-2026-81563
title: >-
  A BIND resolver encountering an SVCB/HTTPS AliasMode record referencing 14 or
  more SVCB/HTTPS ServiceMode records may fail to properly deallocate internal
  resources
summary: >-
  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…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-401
  - CWE-772
vendor: ISC
product: BIND 9
affected:
  - bind_9 >= 9.18.0 <= 9.18.50
  - bind_9 >= 9.20.0 <= 9.20.27
  - bind_9 >= 9.21.0 <= 9.21.25
  - bind_9 >= 9.18.11-S1 <= 9.18.50-S1
  - bind_9 >= 9.20.9-S1 <= 9.20.27-S1
published: '2026-09-16'
updated: '2026-09-17'
sourceUpdated: '2026-09-17T18:17:09.147'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-81563'
references:
  - url: 'https://downloads.isc.org/isc/bind9/9.20.29'
    label: security-officer@isc.org
  - url: 'https://downloads.isc.org/isc/bind9/9.21.26'
    label: security-officer@isc.org
  - url: 'https://kb.isc.org/docs/cve-2026-81563'
    label: security-officer@isc.org
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-81563.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-81563'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2535461'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-81563'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-81563'
  - url: 'https://access.redhat.com/errata/RHSA-2026:68279'
tags:
  - nvd
  - cve.org
  - csaf
  - vex
  - red-hat
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-17T17:47:13.244761Z'
ingestedAt: '2026-09-16T14:57:28.017Z'
epss: 0.00672
epssPercentile: 0.49976
patched:
  - hardened_images
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Vendor advisories

- **Red Hat VEX** · Important · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9 · updated 2026-09-21 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-81563.json)
- **RHSA-2026:68279** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-09-16 · [advisory](https://access.redhat.com/errata/RHSA-2026:68279)