Unchecked Return Value in Junos OS - CVE-2026-21920
Published: January 20, 2026
Vulnerability identifier: #VU121683
CSH Severity: Medium
CVSS v4: 8.7 [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]
CVE-ID: CVE-2026-21920
CWE-ID: CWE-252
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote non-authenticated attacker to perform a denial of service (DoS) attack.
The vulnerability exists due to unchecked return value error in the DNS module. A remote non-authenticated attacker can cause a Denial-of-Service (DoS).
If an SRX Series device configured for DNS processing, receives a specifically formatted DNS request flowd will crash and restart, which causes a service interruption until the process has recovered.
Affected software
Junos OS
How to mitigate CVE-2026-21920
Install updates from vendor's website.
Junos OS - addressed in versions 23.4R2-S5, 24.2R2-S1, 24.4R2, 24.4R2-S1, 25.2R1