Main Vulnerability Database Vulnerabilities #VU121679

Memory leak in Junos OS and Junos OS Evolved - CVE-2026-21909

Published: January 20, 2026

Vulnerability identifier: #VU121679

CSH Severity: Medium

CVSS v4: 7.1 [CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-21909

CWE-ID: CWE-401

Exploitation vector: Adjecent network

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 missing release of memory after effective lifetime error in the routing protocol daemon (rpd). A remote non-authenticated attacker can send a specific update packet causing a memory leak.

Affected software

Junos OS
Junos OS Evolved

How to mitigate CVE-2026-21909

Install updates from vendor's website.

Junos OS - addressed in versions 23.2R2, 23.4R1-S2, 23.4R2, 24.1R2, 24.2R1
Junos OS Evolved - addressed in versions 23.2R2-EVO, 23.4R1-S2-EVO, 23.4R2-EVO, 24.1R2-EVO, 24.2R1-EVO

External References

https://supportportal.juniper.net/s/article/2026-01-Security-Bulletin-Junos-OS-and-Junos-OS-Evolved-Receipt-of-specific-IS-IS-update-packet-causes-memory-leak-leading-to-RPD-crash-CVE-2026-21909

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