Missing Release of Resource after Effective Lifetime in dnsdist - CVE-2026-40209
Published: June 25, 2026
Vulnerability identifier: #VU135339
CSH Severity: Medium
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-40209
CWE-ID: CWE-772
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to missing release of resources after effective lifetime in backend TCP connection handling when processing crafted IXFR queries. A remote attacker can send crafted IXFR queries to cause a denial of service.
Outgoing TCP connections to the backend can remain stuck until a timeout occurs, which can exhaust concurrent backend connections or file descriptors.
Affected software
dnsdist
Debian Linux
dnsdist (Debian package)
Debian Linux
dnsdist (Debian package)
How to mitigate CVE-2026-40209
Install security update from vendor's website.
dnsdist - addressed in versions 1.9.15, 2.0.7
dnsdist (Debian package) - update to 1.9.15-0+deb13u1
dnsdist (Debian package) - update to 1.9.15-0+deb13u1