CVE-2026-21918

Junos OS: SRX and MX Series: When TCP packets occur in a specific sequence flowd crashes

State: Published
Severity: 8.7 High
Published: Jan 15, 2026
Updated: Jan 15, 2026
Reserved: Jan 5, 2026

Description

A Double Free vulnerability in the flow processing daemon (flowd) of Juniper Networks Junos OS on SRX and MX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS). On all SRX and MX Series platforms, when during TCP session establishment a specific sequence of packets is encountered a double free happens. This causes flowd to crash and the respective FPC to restart.

This issue affects Junos OS on SRX and MX Series:

* all versions before 22.4R3-S7, * 23.2 versions before 23.2R2-S3, * 23.4 versions before 23.4R2-S4, * 24.2 versions before 24.2R2.

Scores

CVSS	Score	Vector	Source
4.0	8.7 High	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/AU:Y/R:A/RE:M	juniper
3.1	7.5 High	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H	juniper

Weaknesses

CWE-415 Double Free

Affected Products

Product	Versions
Junos OSJuniper Networks	before 22.4R3-S7Affected 23.2 to before 23.2R2-S3Affected 23.4 to before 23.4R2-S4Affected 24.2 to before 24.2R2Affected

References

https://supportportal.juniper.net/JSA106018vendor-advisory
https://kb.juniper.net/JSA106018vendor-advisory

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