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CVE-2026-21903

6.5 · MEDIUM

A Stack-based Buffer Overflow vulnerability in the Packet Forwarding Engine (pfe) of Juniper Networks Junos OS allows a network-based attacker, authenticated with low privileges to cause a Denial-o…

Published Jan 15, 2026CWE-121EPSS 0.40%

Overview

CVE-2026-21903 is a medium-severity vulnerability. It was published on January 15, 2026 and has a CVSS 3.1 base score of 6.5 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 6.5, rated MEDIUM. It can be exploited remotely over the network. Some level of privileges is required for exploitation.

Technical description

A Stack-based Buffer Overflow vulnerability in the Packet Forwarding Engine (pfe) of Juniper Networks Junos OS allows a network-based attacker, authenticated with low privileges to cause a Denial-of-Service (DoS).

Subscribing to telemetry sensors at scale causes all FPC connections to drop, resulting in an FPC crash and restart.

The issue was not seen when YANG packages for the specific sensors were installed.

This issue affects Junos OS: 

* all versions before 22.4R3-S7,

* 23.2 version before 23.2R2-S4,

* 23.4 versions before 23.4R2.

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/JSA106022Refsupportportal.juniper.net/JSA106022

How CyberStrike helps

Frequently asked questions

What is CVE-2026-21903?

CVE-2026-21903 is a medium-severity vulnerability. It was published on January 15, 2026 and has a CVSS 3.1 base score of 6.5 (MEDIUM).

How severe is CVE-2026-21903?

This vulnerability has a CVSS 3.1 base score of 6.5, rated MEDIUM. It can be exploited remotely over the network. Some level of privileges is required for exploitation.

How do I fix or remediate CVE-2026-21903?

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-2026-21903?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-21903 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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