CVE-2026-55717 Affecting unbound package, versions <0:1.17.1-1.amzn2023.0.13
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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Test your applications- Snyk IDSNYK-AMZN2023-UNBOUND-18530801
- published5 Aug 2026
- disclosed22 Jul 2026
Introduced: 22 Jul 2026
NewCVE-2026-55717 (opens in a new tab)How to fix?
Upgrade Amazon-Linux:2023 unbound to version 0:1.17.1-1.amzn2023.0.13 or higher.
This issue was patched in ALAS2023-2026-2033.
NVD Description
Note: Versions mentioned in the description apply only to the upstream unbound package and not the unbound package as distributed by Amazon-Linux.
See How to fix? for Amazon-Linux:2023 relevant fixed versions and status.
In NLnet Labs Unbound 1.10.0 up to and including 1.25.1, when 'serve-expired: yes' is set together with a 'response-ip: <net> redirect' /'response-ip-data: <net> CNAME <target>' rule (or the RPZ 'rpz-cname-override' equivalent), a remote client who controls any delegated domain can crash the daemon. The serve-expired-client-timeout callback runs a two-pass loop to chase the respip-generated CNAME alias; on the second pass it resets 'alias_rrset' but not 'partial_rep'. Later, this inconsistency leads to a NULL pointer dereference and an eventual crash. A malicious actor can exploit the vulnerability by controlling any zone that replies with an A/AAAA record that falls inside the configured response-ip/rpz subnet. By delaying the answer when the previous record has expired, the vulnerable path of 'serve-expired-client-timeout' is taken leading to denial of service via the server crash.