Stack-based buffer overflow in Unbound - CVE-2026-55973
Published: July 23, 2026
Vulnerability identifier: #VU139222
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: CVE-2026-55973
CWE-ID: CWE-121
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: NLnet Labs
Affected software:
Unbound
Unbound
Detailed vulnerability description
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to a stack-based buffer overflow in find_closest_of_type() when processing a crafted upstream DNS response containing an EDNS Report-Channel option. A remote attacker can send a specially crafted upstream response from a delegated zone they control to cause a denial of service.
The issue is reachable only when 'dns-error-reporting: yes' is enabled.
How to mitigate CVE-2026-55973
Install security update from vendor's website.