DoS via Unchecked Loop in Juniper Junos OS pfe on MX Series (pre-25.2R2)
CVE-2026-33800 Published on July 9, 2026
Junos OS: MX Series: In a VC scenario a high rate of micro-BFD session flaps will cause an FPC crash
An Unchecked Input for Loop Condition vulnerability in the Packet Forwarding Engine (pfe) of Juniper Networks Junos OS on MX Series allows an unauthenticated, adjacent attacker to cause a Denial-of-Service (DoS).Micro-BFD session flaps generate respective up/down events which are queued by PFEMAN for processing. Especially in a Virtual-Chassis (VC) scenario with localitybias configured, processing takes a significant amount of time for each event. If these sessions keep flapping, new events are constantly added, and in turn PFEMAN never completes processing these events. This results in the PFEMAN watchdog timer expiring, which causes the FPC to crash and restart, representing a complete service outage.
This issue only affects MX series FPCs up to and including MPC9, and LC2101/2103 and LC480. It does not affect MPC10/11, LC4800/9600, and MX304.
This issue affects Junos OS on MX Series:
* all versions before 23.2R2-S7,
* 23.4 versions before 23.4R2-S8,
* 24.2 versions before 24.2R2-S4,
* 24.4 versions before 24.4R2-S3,
* 25.2 versions before 25.2R2.
Vulnerability Analysis
Weakness Type
Unchecked Input for Loop Condition
The product does not properly check inputs that are used for loop conditions, potentially leading to a denial of service or other consequences because of excessive looping.
Products Associated with CVE-2026-33800
Want to know whenever a new CVE is published for Juniper Networks Junos? stack.watch will email you.
Affected Versions
Juniper Networks Junos OS:- Before 23.2R2-S7 is affected.
- Version 23.4 and below 23.4R2-S8 is affected.
- Version 24.2 and below 24.2R2-S4 is affected.
- Version 24.4 and below 24.4R2-S3 is affected.
- Version 25.2 and below 25.2R2 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.