Juniper Junos OS pfe Stack Overflow DoS (<22.4R3, <23.2R2, <23.4R2)
CVE-2026-21903 Published on January 15, 2026
Junos OS: Subscribing to telemetry sensors at scale causes all FPCs to crash
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.
Vulnerability Analysis
CVE-2026-21903 can be exploited with network access, and requires small amount of user privileges. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a high impact on availability.
Weakness Type
What is a Stack Overflow Vulnerability?
A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).
CVE-2026-21903 has been classified to as a Stack Overflow vulnerability or weakness.
Products Associated with CVE-2026-21903
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Affected Versions
Juniper Networks Junos OS:- Before 22.4R3-S7 is affected.
- Version 23.2 and below 23.2R2-S4 is affected.
- Version 23.4 and below 23.4R2 is affected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.