# CVE-2024-39561: Security feature bypass in Junos OS

> Attackers can bypass TCP packet filtering on Juniper SRX devices by sending SYN/FIN or SYN/RST packets when specific non-default features are enabled.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 10 Jul 2024
- **Updated:** 2 Aug 2024
- **Also known as:** GHSA-xvm6-65jm-mc4g

## What is CVE-2024-39561?

CVE-2024-39561 is a medium-severity vulnerability in Juniper Junos, published on 10 Jul 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-754 (Improper Check for Unusual or Exceptional Conditions)

## Which versions are affected by CVE-2024-39561?

It affects 1 product.


Products: Juniper Junos.

## How do I fix CVE-2024-39561?

No fix has been published for CVE-2024-39561 yet. Limit exposure of the affected software until one is available.

## Is CVE-2024-39561 being exploited?

There is no known exploitation of CVE-2024-39561 in the wild and no public exploit code.

## Other vulnerabilities in Juniper Junos

- [CVE-2023-36845](https://insights.sbomify.com/CVE-2023-36845/): Juniper Junos OS EX Series and SRX Series PHP External Variable Modification (critical 9.8, exploited in the wild)
- [CVE-2020-1631](https://insights.sbomify.com/CVE-2020-1631/): Juniper Junos OS Path Traversal (high 8.8, exploited in the wild)
- [CVE-2025-21590](https://insights.sbomify.com/CVE-2025-21590/): Juniper Junos OS Improper Isolation or Compartmentalization (medium 6.7, exploited in the wild)
- [CVE-2023-36851](https://insights.sbomify.com/CVE-2023-36851/): Juniper Junos OS SRX Series Missing Authentication for Critical Function (medium 5.3, exploited in the wild)
- [CVE-2023-36844](https://insights.sbomify.com/CVE-2023-36844/): Juniper Junos OS EX Series PHP External Variable Modification (medium 5.3, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2024-39561 and fix it if it is affected.

What it is: CVE-2024-39561 is a medium-severity vulnerability in Juniper Junos, published on 10 Jul 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2024-39561 in the wild and no public exploit code.

Affected product: Juniper Junos. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2024-39561/ (Markdown: https://insights.sbomify.com/CVE-2024-39561/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-39561
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-39561
- OSV: https://osv.dev/vulnerability/CVE-2024-39561

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-39561/
Summaries are generated and may contain mistakes; the official description above is the record.