---
id: CVE-2026-82720
title: >-
  NLnet Labs Unbound 1.12.0 up to and including 1.26.0 has a use-after-free
  vulnerability when compiled for DNS-over-HTTPs support with
  '--with-libnghttp2'
summary: >-
  NLnet Labs Unbound 1.12.0 up to and including 1.26.0 has a use-after-free
  vulnerability when compiled for DNS-over-HTTPs support with
  '--with-libnghttp2'. During failure code paths (i.e., RPZ drop query, jostle
  due to heavy traffic), a d…
severity: medium
cvss: 5.9
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-416
  - CWE-825
vendor: nlnetlabs
product: unbound
affected:
  - 'unbound >= 1.12.0, < 1.26.1'
patched:
  - unbound 1.26.1
published: '2026-09-16'
updated: '2026-09-23'
sourceUpdated: '2026-09-23T19:49:08.910'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-82720'
references:
  - url: 'https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-82720.txt'
    label: sep@nlnetlabs.nl
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-82720.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-82720'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2535060'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-82720'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-82720'
  - url: 'https://access.redhat.com/errata/RHSA-2026:68590'
tags:
  - nvd
  - cve.org
  - csaf
  - vex
  - red-hat
epss: 0.00382
epssPercentile: 0.29548
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-16T14:13:03.616721Z'
ingestedAt: '2026-09-16T08:52:29.597Z'
---

## Overview

NLnet Labs Unbound 1.12.0 up to and including 1.26.0 has a use-after-free vulnerability when compiled for DNS-over-HTTPs support with '--with-libnghttp2'. During failure code paths (i.e., RPZ drop query, jostle due to heavy traffic), a dropped DoH stream brings down the whole DoH session and does not account properly for other DoH streams in the same session. This leads to use-after-free in those code paths. If the prerequisites are satisfied (possible RPZ drop or heavy client traffic), a malicious actor can trigger the vulnerability with a single DoH connection and the appropriate traffic. Impact is limited as the reads are not user controlled and the use-after-free leads to early returns. However, a hardened allocator can catch the use-after-free and controllably terminate the process resulting to denial of service.

## Affected

- `unbound >= 1.12.0, < 1.26.1`

## Remediation

Upgrade past the affected range:

- `unbound 1.26.1`

## Vendor advisories

- **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · updated 2026-09-21 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-82720.json)
- **RHSA-2026:68590** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-09-17 · [advisory](https://access.redhat.com/errata/RHSA-2026:68590)