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CVE-2026-21918

7.5 · HIGH

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 (D…

Published Jan 15, 2026CWE-415EPSS 0.41%

Overview

CVE-2026-21918 is a high-severity vulnerability. It was published on January 15, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

Refkb.juniper.net/JSA106018Refsupportportal.juniper.net/JSA106018

How CyberStrike helps

Frequently asked questions

What is CVE-2026-21918?

CVE-2026-21918 is a high-severity vulnerability. It was published on January 15, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-21918?

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-21918?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-21918?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-21918 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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