CVE-2026-33800: 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 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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Juniper Networks Junos OS (MX Series)to a version that resolves this vulnerability.Fixed in 23.2R2-S7 - Upgrade
Upgrade
Juniper Networks Junos OS (MX Series)to a version that resolves this vulnerability.Fixed in 23.4R2-S8 - Upgrade
Upgrade
Juniper Networks Junos OS (MX Series)to a version that resolves this vulnerability.Fixed in 24.2R2-S4 - Upgrade
Upgrade
Juniper Networks Junos OS (MX Series)to a version that resolves this vulnerability.Fixed in 24.4R2-S3 - Upgrade
Upgrade
Juniper Networks Junos OS (MX Series)to a version that resolves this vulnerability.Fixed in 25.2R2 - Upgrade
Upgrade
Juniper Networks Junos OS (MX Series)to a version that resolves this vulnerability.Fixed in 25.4R1
Event History
Frequently Asked Questions
What is the severity of CVE-2026-33800?
The severity of CVE-2026-33800 is medium with a CVSS score of 6.5.
How does CVE-2026-33800 affect Junos OS on MX Series?
CVE-2026-33800 allows an unauthenticated, adjacent attacker to cause a Denial-of-Service (DoS) by exploiting high rates of micro-BFD session flaps.
What are the potential impacts of CVE-2026-33800?
The potential impact of CVE-2026-33800 includes the crashing of the FPC, leading to network service disruptions.
How can I mitigate CVE-2026-33800?
Mitigation for CVE-2026-33800 involves applying the latest patches and following best practices for network security.
Is CVE-2026-33800 exploitable remotely?
No, CVE-2026-33800 requires an adjacent attacker to exploit the vulnerability.