NLnet Labs Unbound up to 1.25.1 Function Call Allow List libworker_alloc_cleanup unwanted-reply-threshold input validation

Summaryinfo

A vulnerability labeled as problematic has been found in NLnet Labs Unbound up to 1.25.1. The affected element is the function libworker_alloc_cleanup of the component Function Call Allow List. Such manipulation of the argument unwanted-reply-threshold leads to input validation. This vulnerability is uniquely identified as CVE-2026-44621. The attack can be launched remotely. No exploit exists.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in NLnet Labs Unbound up to 1.25.1. Affected by this issue is the function libworker_alloc_cleanup of the component Function Call Allow List. The manipulation of the argument unwanted-reply-threshold with an unknown input leads to a input validation vulnerability. Using CWE to declare the problem leads to CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. Impacted is availability. CVE summarizes:

With NLnet Labs Unbound up to and including version 1.25.1, applications using libunbound and configured with 'unwanted-reply-threshold', could eventually be abruptly terminated if the threshold is reached and libunbound needs to call 'libworker_alloc_cleanup' since the function is absent from the function call allow list. When an application using libunbound sets 'unwanted-reply-threshold' to any non-zero value and the iterator queries an authoritative that replies with enough wrong-transaction-ID UDP datagrams to cross the threshold, the 'libworker_alloc_cleanup' will eventually be called. Since the function is absent from the function call allow list, this leads to a fatal exit of libunbound and eventual termination of the embedding application.Unbound itself is not affected since its relevant function 'worker_alloc_cleanup' is registed in the allow list and proceeds to perform the documented cache flush.

The advisory is available at nlnetlabs.nl. This vulnerability is handled as CVE-2026-44621 since 06/22/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. Technical details are known, but there is no available exploit.

Upgrading to version 1.25.2 eliminates this vulnerability.

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

Productinfo

Vendor

• NLnet Labs

Name

• Unbound

Version

• 1.25.0
• 1.25.1

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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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