# CVE-2024-39540: Junos OS: SRX Series, and MX Series with SPC3: Specific valid TCP traffic can cause a pfe crash

> An unauthenticated attacker can cause a Packet Forwarding Engine crash and service outage on Juniper SRX and MX devices by sending specific valid TCP traffic.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 11 Jul 2024
- **Updated:** 2 Aug 2024
- **Also known as:** GHSA-xwcp-g9fq-2mmp

## What is CVE-2024-39540?

CVE-2024-39540 is a high-severity denial of service vulnerability in Juniper Junos, published on 11 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 Packet Forwarding Engine (pfe) of Juniper Networks Junos OS on SRX Series, and MX Series with SPC3 allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS).

When an affected device receives specific valid TCP traffic, the pfe crashes and restarts leading to a momentary but complete service outage.

This issue affects Junos OS:

21.2 releases from 21.2R3-S5 before 21.2R3-S6.

This issue does not affect earlier or later releases.

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

## Which versions are affected by CVE-2024-39540?

It affects 1 product.


Products: Juniper Junos.

## How do I fix CVE-2024-39540?

No fix has been published for CVE-2024-39540 yet. Limit exposure of the affected software until one is available.

## Is CVE-2024-39540 being exploited?

There is no known exploitation of CVE-2024-39540 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-2024-39540 and fix it if it is affected.

What it is: CVE-2024-39540 is a high-severity denial of service vulnerability in Juniper Junos, published on 11 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-2024-39540 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-2024-39540/ (Markdown: https://insights.sbomify.com/CVE-2024-39540/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-39540
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-39540
- OSV: https://osv.dev/vulnerability/CVE-2024-39540

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-39540/
Summaries are generated and may contain mistakes; the official description above is the record.