Log in Start free

Vulnerability · Published Sep 16, 2026 · Assigned by NLnet Labs

CVE-2026-82720Use-after-free in DoH stream cleanup code path

Medium 5.9

In plain English

A medium-severity use-after-free in Unbound from NLnet Labs. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 32% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.9Medium
Exploit odds (30 days)0.4%top 67.5% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

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 packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12unboundno fix listedDEBIAN-CVE-2026-82720
Debian:13unbound1.26.1-0+deb13u1DEBIAN-CVE-2026-82720
Debian:14unbound1.26.1-1DEBIAN-CVE-2026-82720
Ubuntu:22.04:LTSunboundno fix listedUBUNTU-CVE-2026-82720
Ubuntu:24.04:LTSunboundno fix listedUBUNTU-CVE-2026-82720
Ubuntu:26.04:LTSunboundno fix listedUBUNTU-CVE-2026-82720
Ubuntu:26.10unboundno fix listedUBUNTU-CVE-2026-82720

Affected products (as reported)

VendorProductVersions
NLnet Labs Unbound 1.12.0 – before 1.26.1

Weakness: CWE-416 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

References