CVE-2026-33278
CriticalCVSS 9.8Exploitation Probability (EPSS)
Elevated risk66th percentile — higher than 66% of all known CVEs
Summary
In Unbound 1.19.1 up to 1.25.0, a vulnerability in the DNSSEC validator allows denial of service and potential remote code execution. The bug occurs due to improper deep copying of a data structure, overwriting the destination pointer with the source pointer. After sub-query memory is freed, the resumed validator dereferences a dangling pointer, causing a crash or potentially enabling arbitrary code execution.
Risk Assessment
The organization is at risk of DoS attacks and potential remote code execution by an attacker controlling a malicious signed zone. This could lead to DNS service disruption and server compromise.
Recommendation
Immediately update Unbound to version 1.25.1 or later, which includes a fix for the data structure copying bug.
Original NVD description (English source)
NLnet Labs Unbound 1.19.1 up to and including version 1.25.0 has a vulnerability in the DNSSEC validator that enables denial of service and possible remote code execution as a result of deep copying a data structure and erroneously overwriting a destination pointer. An adversary can exploit the vulnerability by controlling a malicious signed zone and querying a vulnerable Unbound. When DS sub-queries need to suspend validation due to NSEC3 computational budget exhaustion (introduced in Unbound 1.19.1), Unbound deep-copies response messages to preserve them across memory region teardown. A struct-assignment bug overwrites the destination's pointer with the source's pointer. After the sub-query region is freed, the resumed validator dereferences this dangling pointer, triggering a crash or potentially enabling arbitrary code execution. Unbound 1.25.1 contains a patch with a fix to preserve the correct pointer when deep copying the data structure.