Quick answers
- Is CVE-2026-55717 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-55717 being exploited in the wild.
- How severe is CVE-2026-55717?
- Medium severity, with a CVSS score of 5.9, published 22 July 2026.
- Which products and versions are affected?
- NLnet Labs Unbound 1.10.0 to 1.25.1.
- Is there a fix for CVE-2026-55717?
- A patch was published on 2026-07-22: Fixed in version 1.25.2 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-55717 attacked?
- It is attacked over the network, in a hosted service.
- Am I affected by CVE-2026-55717?
- Check whether you run NLnet Labs Unbound at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
A NULL pointer dereference exists in the 'serve-expired-client-timeout' callback of NLnet Labs Unbound. When 'serve-expired' is enabled alongside 'response-ip' redirect or RPZ CNAME override rules, the callback's two-pass loop for chasing CNAME aliases fails to reset the 'partial_rep' pointer during the second pass, despite resetting 'alias_rrset'. An attacker controlling a delegated domain can trigger this inconsistency by returning an A/AAAA record within a configured response-ip subnet and delaying the response to force the 'serve-expired' code path. This leads to a daemon crash. The issue is fixed in Unbound version 1.25.2.
Affected products
- NLnet Labs Unbound 1.10.0 to 1.25.1
Timeline
- 2026-07-22: disclosed
- 2026-07-22: advisory
- 2026-07-22: patched: Fixed in version 1.25.2