CVE Catalog

CVE-2026-55973

HighCVSS 7.5
Published: Updated: Translated: NVD NIST

Exploitation Probability (EPSS)

Low risk
0.29%

21th percentile - higher than 21% of all known CVEs

Summary

Vulnerability in NLnet Labs Unbound (versions 1.23.0 to 1.25.1) with 'dns-error-reporting: yes' enabled allows an attacker to remotely crash the daemon by sending a crafted upstream response. The bug occurs when processing the EDNS Report-Channel option.

Risk Assessment

The attack can cause a DNS server denial of service, disrupting network services.

Recommendation

Disable 'dns-error-reporting' or upgrade Unbound to a patched version.

Related vulnerabilities

Original NVD description (English source)

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.

Vulnerability data from NVD (NIST) · CISA KEV · EPSS