CVE-2026-33278

Summary

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.

Affected Software

VendorProductVersion RangeStatus
NLnet LabsUnbound1.19.1 < 1.25.1affected

Weaknesses

  • CWE-416: CWE-416: Use After Free
  • CWE-672: CWE-672: Operation on a Resource after Expiration or Release

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: yes
    • Technical Impact: total

unbound: Unbound DNSSEC Validator Use-After-Free via Deep Copy Pointer Overwrite Leading to DoS and Possible Remote Code Execution

Additional References

References