Juniper Junos OS up to 22.4R3-S6/23.2R2-S2/23.4R2-S3/24.2R1 on SRX Flow Handler Daemon double free

Summaryinfo

A vulnerability categorized as critical has been discovered in Juniper Junos OS up to 22.4R3-S6/23.2R2-S2/23.4R2-S3/24.2R1 on SRX. This vulnerability affects unknown code of the component Flow Handler Daemon. The manipulation results in double free. This vulnerability is cataloged as CVE-2026-21918. The attack may be launched remotely. There is no exploit available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, was found in Juniper Junos OS up to 22.4R3-S6/23.2R2-S2/23.4R2-S3/24.2R1 on SRX. Affected is an unknown functionality of the component Flow Handler Daemon. The manipulation with an unknown input leads to a double free vulnerability. CWE is classifying the issue as CWE-415. The product calls free() twice on the same memory address, potentially leading to modification of unexpected memory locations. This is going to have an impact on availability. CVE summarizes:

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.

The advisory is available at supportportal.juniper.net. This vulnerability is traded as CVE-2026-21918 since 01/05/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. The technical details are unknown and an exploit is not available. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 01/16/2026).

Upgrading to version 22.4R3-S7, 23.2R2-S3, 23.4R2-S4 or 24.2R2 eliminates this vulnerability.

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Productinfo

Type

• Router Operating System

Vendor

• Juniper

Name

• Junos OS

Version

• 22.4R3-S6
• 23.2R2-S2
• 23.4R2-S3
• 24.2R1

License

• commercial

Website

• Vendor: https://www.juniper.net/

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