CVE-2026-33800
published 2026-07-09CVE-2026-33800: An Unchecked Input for Loop Condition vulnerability in the Packet Forwarding Engine (pfe) of Juniper Networks Junos OS on MX Series allows an unauthenticated…
PriorityP432medium6.5CVSS 3.1
AVAACLPRNUINSUCNINAH
EPSS
0.27%
18.7th percentile
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. 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
5 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| juniper_networks | junos_os | < 23.2R2-S7 | 23.2R2-S7 |
| juniper_networks | junos_os | >= 23.4 < 23.4R2-S8 | 23.4R2-S8 |
| juniper_networks | junos_os | >= 24.2 < 24.2R2-S4 | 24.2R2-S4 |
| juniper_networks | junos_os | >= 24.4 < 24.4R2-S3 | 24.4R2-S3 |
| juniper_networks | junos_os | >= 25.2 < 25.2R2 | 25.2R2 |
CVSS provenance
nvdv3.16.5MEDIUMCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
nvdv4.07.1HIGHCVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:Y/R:A/V:X/RE:M/U:X
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GHSA
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-Se
ghsa_unreviewed·2026-07-09
CVE-2026-33800 [HIGH] CWE-606 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-Se
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. It does not affect
VulDB
Juniper Junos OS up to 25.2R1 Packet Forwarding Engine infinite loop
vuldb·2026-07-09·CVSS 6.5
CVE-2026-33800 [MEDIUM] Juniper Junos OS up to 25.2R1 Packet Forwarding Engine infinite loop
A vulnerability marked as problematic has been reported in Juniper Junos OS up to 23.2R2-S6/23.4R2-S7/24.2R2-S3/24.4R2-S2/25.2R1. Affected by this vulnerability is an unknown functionality of the component Packet Forwarding Engine. This manipulation causes infinite loop.
This vulnerability is handled as CVE-2026-33800. It is possible to launch the attack on the local host. There is not any exploit available.
No detection rules found.
No public exploits indexed.
No writeups or analysis indexed.
2026-07-09
Published