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Vulnerability · Published Jul 22, 2026 · Assigned by NLnet Labs

CVE-2026-50046Possible heap use-after-free in an error path when a DoT forwarded query is jostled out

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 0.2% (higher than 15% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.9Medium
Exploit odds (30 days)0.2%top 85.2% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

In NLnet Labs Unbound 1.15.0 up to and including 1.25.1, the TLS server name used for DNS-over-TLS (DoT) forwarded queries is tied to a struct's ('serviced_query') lifetime but also referenced by another struct ('waiting_tcp'). When the owning struct is jostled out of the mesh while the DoT TCP stream is still handshaking it frees the storage behind the referenced string and if the TLS stream then errors out, it dereferences the freed pointer. The dereference is read-only and the practical impact is a daemon crash resulting in denial of service. A malicious actor that knows a DoT forwarding/stub Unbound's configuration could exploit the vulnerability by quering records in the appropriate zone while keeping Unbound uder pressure so that the jostle logic kicks in. If answers for the vulnerable zone are slow, the likelihood of jostling such queries is higher, although the timing of the jostle needs to be precise. Requirements for a vulnerable Unbound is the existence of a stub/forward zone configured for DoT together with a configured '#authname' suffix on the server identification. The connectivity to the server needs to exhibit a transient failure at the correct time in order to kick off the vulnerable error path.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Alpine:v3.22unbound1.25.2-r0ALPINE-CVE-2026-50046
Alpine:v3.23unbound1.25.2-r0ALPINE-CVE-2026-50046
Alpine:v3.24unbound1.25.2-r0ALPINE-CVE-2026-50046
Debian:12unboundno fix listedDEBIAN-CVE-2026-50046
Debian:13unbound1.26.1-0+deb13u1DEBIAN-CVE-2026-50046
Debian:14unbound1.25.2-1DEBIAN-CVE-2026-50046
Ubuntu:22.04:LTSunboundno fix listedUBUNTU-CVE-2026-50046
Ubuntu:24.04:LTSunboundno fix listedUBUNTU-CVE-2026-50046
Ubuntu:26.04:LTSunboundno fix listedUBUNTU-CVE-2026-50046
Ubuntu:26.10unboundno fix listedUBUNTU-CVE-2026-50046

Affected products (as reported)

VendorProductVersions
NLnet Labs Unbound 1.15.0 – before 1.25.2

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

References