NLnet Labs Unbound up to 1.25.1 DoT Forwarding use after free

Summaryinfo

A vulnerability was found in NLnet Labs Unbound up to 1.25.1 and classified as critical. This vulnerability affects unknown code of the component DoT Forwarding. Executing a manipulation can lead to use after free. This vulnerability is registered as CVE-2026-50046. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability classified as critical was found in NLnet Labs Unbound up to 1.25.1. This vulnerability affects an unknown code of the component DoT Forwarding. The manipulation with an unknown input leads to a use after free vulnerability. The CWE definition for the vulnerability is CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. As an impact it is known to affect availability. CVE summarizes:

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.

The advisory is available at nlnetlabs.nl. This vulnerability was named CVE-2026-50046 since 06/22/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. The technical details are unknown and an exploit is not available.

Upgrading to version 1.25.2 eliminates this vulnerability.

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Productinfo

Vendor

• NLnet Labs

Name

• Unbound

Version

• 1.25.0
• 1.25.1

CPE 2.3info

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CPE 2.2info

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If you want to get best quality of vulnerability data, you may have to visit VulDB.

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