# CVE-2024-39542: Junos OS and Junos OS Evolved: A malformed CFM packet or specific transit traffic leads to FPC crash

> An unauthenticated attacker can crash the Packet Forwarding Engine via malformed CFM packets or specific transit traffic, causing a denial of service.

- **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-34f4-m9rh-9x9j

## What is CVE-2024-39542?

CVE-2024-39542 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 Validation of Syntactic Correctness of Input vulnerability in the Packet Forwarding Engine (PFE) of Juniper Networks Junos OS on MX Series with MPC10/11 or LC9600, MX304, and Junos OS Evolved on ACX Series and PTX Series allows an unauthenticated, network based attacker to cause a Denial-of-Service (DoS).

This issue can occur in two scenarios:

1. If a device, which is configured with SFLOW and ECMP, receives specific valid transit traffic, which is subject to sampling, the packetio process crashes, which in turn leads to an evo-aftman crash and causes the FPC to stop working until it is restarted. (This scenario is only applicable to PTX but not to ACX or MX.)

2. If a device receives a malformed CFM packet on an interface configured with CFM, the packetio process crashes, which in turn leads to an evo-aftman crash and causes the FPC to stop working until it is restarted. Please note that the CVSS score is for the formally more severe issue 1.

The CVSS score for scenario 2. is: 6.5 (CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

This issue affects Junos OS:

  *  All versions before 21.2R3-S4,
  *  21.4 versions before 21.4R2,
  *  22.2 versions before 22.2R3-S2; 

Junos OS Evolved:

  *  All versions before 21.2R3-S8-EVO,
  *  21.4 versions before 21.4R2-EVO.

Weakness: CWE-1286 (Improper Validation of Syntactic Correctness of Input)

## Which versions are affected by CVE-2024-39542?

It affects 2 products.


Products: Juniper Junos, Juniper Junos Os Evolved.

## How do I fix CVE-2024-39542?

No fix has been published for CVE-2024-39542 yet. Limit exposure of the affected software until one is available.

## Is CVE-2024-39542 being exploited?

There is no known exploitation of CVE-2024-39542 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-2024-39542 and fix it if it is affected.

What it is: CVE-2024-39542 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-2024-39542 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-2024-39542/ (Markdown: https://insights.sbomify.com/CVE-2024-39542/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-39542
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-39542
- OSV: https://osv.dev/vulnerability/CVE-2024-39542

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-39542/
Summaries are generated and may contain mistakes; the official description above is the record.