CVE-2026-55973 Affecting unbound package, versions <1.25.2-160000.1.1


Severity

Recommended
0.0
high
0
10

Based on SUSE Linux Enterprise Server security rating.

Threat Intelligence

EPSS
0.46% (38th percentile)

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  • Snyk IDSNYK-SLES1600-UNBOUND-19289631
  • published27 Aug 2026
  • disclosed10 Aug 2026

Introduced: 10 Aug 2026

CVE-2026-55973  (opens in a new tab)

How to fix?

Upgrade SLES:16.0.0 unbound to version 1.25.2-160000.1.1 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 SLES. See How to fix? for SLES:16.0.0 relevant fixed versions and status.

In NLnet Labs Unbound 1.23.0 up to and including 1.25.1, when 'dns-error-reporting: yes' is set, the EDNS Report-Channel option (code 18) from the last upstream response is read and uses the option's length as the length of the agent domain. When a domain name check is performed on the agent domain, the returned lenght is not used and if the agent domain is followed by garbage, those bytes are moved onto the tail of the synthetic '_er.' report query name. That query name is later used in the iterator via a subquery to send out the DNS Error Report and when Unbound tries to walk that query name during 'find_closest_of_type()', it strips labels using the query name length rather than stopping at the embedded root, walks one byte past it, and feeds the first garbage byte to 'dname_query_hash()' as a label length writing over the stack variable 'labuf'. One ordinary upstream response from a delegated zone the attacker controls is sufficient to terminate the daemon.

CVSS Base Scores

version 3.1