Reachable assertion in ISC BIND - CVE-2025-40777
Published: July 17, 2025
Vulnerability identifier: #VU113026
CSH Severity: Medium
CVSS v4: 8.2 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2025-40777
CWE-ID: CWE-617
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.
The vulnerability exists due to a reachable assertion when named caching resolver is configured with "serve-stale-enable=yes" and "stale-answer-client-timeout=0". A remote attacker can supply a specially crafted CNAME chain in DNS response and perform a denial of service attack against the resolver.
Affected software
ISC BIND
Ubuntu
bind9 (Ubuntu package)
Ubuntu
bind9 (Ubuntu package)
How to mitigate CVE-2025-40777
Install updates from vendor's website.
ISC BIND - addressed in versions 9.20.11, 9.20.11-S1, 9.21.10
bind9 (Ubuntu package) - update to 1:9.20.4-3ubuntu1.2
bind9 (Ubuntu package) - update to 1:9.20.4-3ubuntu1.2