Junos OS (SRX firewalls)
CVE-2026-33800: 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.
Published
Automatic summary from the vendor's CVE record. We haven't written a full analysis of this vulnerability yet.
Affected and fixed versions
| Product / branch | Fixed in |
|---|---|
| Junos OS (MX Series) 0 | 23.2R2-S7 or later |
| Junos OS (MX Series) 23.4 | 23.4R2-S8 or later |
| Junos OS (MX Series) 24.2 | 24.2R2-S4 or later |
| Junos OS (MX Series) 24.4 | 24.4R2-S3 or later |
| Junos OS (MX Series) 25.2 | 25.2R2 or later |
Always confirm against the vendor advisory, which lists every fixed hotfix.
What it is
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 locality‑bias 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.
Am I affected?
To be exposed to this issue an MX VC needs to be configured with locality bias as follows:
[ virtual-chassis locality-bias ]
Workarounds
To reduce the risk of exploitation, configure BFD with an increased holddown-timer, so that the queued events can be processed before a new up event occurs:
[ ... bfd-liveness-detection holddown-interval milliseconds <value> ]
Exploitation
Juniper SIRT is not aware of any malicious exploitation of this vulnerability.
Sources
KEV status, EPSS score and vendor data refreshed automatically, last on 13 Oct 2026.