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CVE-2026-21917

7.5 · HIGH

An Improper Validation of Syntactic Correctness of Input vulnerability in the Web-Filtering module of Juniper Networks Junos OS on SRX Series allows an unauthenticated, network-based attacker to ca…

Published Jan 15, 2026CWE-1286EPSS 0.41%

Overview

CVE-2026-21917 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

An Improper Validation of Syntactic Correctness of Input vulnerability in the Web-Filtering module of Juniper Networks Junos OS on SRX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS).

If an SRX device configured for UTM Web-Filtering receives a specifically malformed SSL packet, this will cause an FPC crash and restart.

This issue affects Junos OS on SRX Series:

* 23.2 versions from 23.2R2-S2 before 23.2R2-S5, 

* 23.4 versions from 23.4R2-S1 before 23.4R2-S5,

* 24.2 versions before 24.2R2-S2,

* 24.4 versions before 24.4R1-S3, 24.4R2.

Earlier versions of Junos are also affected, but no fix is available.

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/JSA105996Refsupportportal.juniper.net/JSA105996

How CyberStrike helps

Frequently asked questions

What is CVE-2026-21917?

CVE-2026-21917 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-2026-21917?

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-2026-21917?

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-2026-21917?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-21917 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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