CVE-2026-56444 Affecting unbound package, versions <1.25.2
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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- published23 Jul 2026
- disclosed22 Jul 2026
Introduced: 22 Jul 2026
NewCVE-2026-56444 (opens in a new tab)How to fix?
Upgrade Echo:latest unbound to version 1.25.2 or higher.
NVD Description
Note: Versions mentioned in the description apply only to the upstream unbound package and not the unbound package as distributed by Echo.
See How to fix? for Echo:latest relevant fixed versions and status.
In NLnet Labs Unbound 1.20.0 up to and including 1.25.1, when Unbound is configured with 'serve-expired: yes' and 'serve-expired-client-timeout > discard-timeout > 0' (contrary to the suggested values), the discard-timeout branch during the serve expired logic drops an aged client reply without performing the correct accounting for the number of reply addresses for the query. Other identical branches outside of serve expired perform the correct decrement. Since the counter is never decremented in such scenario, it can reach the maximum limit and new clients for duplicate in-flight queries are silently dropped resulting in degradation of resolution service. A malicious actor can exploit the vulnerability by querying the resolver for a client-controlled slow-on-demand authoritative zone that can drive the counter past the threshold. Shipped defaults for 'serve-expired-client-timeout: 1800' and 'discard-timeout: 1900' make the branch unreachable.