Improper handling of exceptional conditions in Unbound - CVE-2026-50251
Published: July 23, 2026
Vulnerability identifier: #VU139228
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-2026-50251
CWE-ID: CWE-755
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 improper handling of unwanted replies in the iterator when processing in-bailiwick glue records of 0.0.0.0/::0 with 'unwanted-reply-threshold' enabled. A remote attacker can control a delegation that returns crafted glue records to cause a denial of service.
The issue can repeatedly trigger defensive clearing of the message and rrset caches, and does not require sending spoofed packets.
How to mitigate CVE-2026-50251
Install security update from vendor's website.