# CVE-2024-21600: Junos OS: PTX Series: In an FTI scenario MPLS packets hitting reject next-hop will cause a host path wedge condition

> Unauthenticated adjacent attackers can cause a denial of service on Juniper PTX routers by sending MPLS packets to a downed flexible tunnel interface.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 12 Jan 2024
- **Updated:** 17 Jun 2025
- **Also known as:** GHSA-8f5g-v4g5-c448

## What is CVE-2024-21600?

CVE-2024-21600 is a medium-severity denial of service vulnerability in Juniper Junos, published on 12 Jan 2024. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

An Improper Neutralization of Equivalent Special Elements vulnerability in the Packet Forwarding Engine (PFE) of Juniper Networks Junos OS on PTX Series allows a unauthenticated, adjacent attacker to cause a Denial of Service (DoS).

When MPLS packets are meant to be sent to a flexible tunnel interface (FTI) and if the FTI tunnel is down, these will hit the reject NH, due to which the packets get sent to the CPU and cause a host path wedge condition. This will cause the FPC to hang and requires a manual restart to recover.

Please note that this issue specifically affects PTX1000, PTX3000, PTX5000 with FPC3, PTX10002-60C, and PTX10008/16 with LC110x. Other PTX Series devices and Line Cards (LC) are not affected.

The following log message can be seen when the issue occurs:

Cmerror Op Set: Host Loopback: HOST LOOPBACK WEDGE DETECTED IN PATH ID <id> (URI: /fpc/<fpc>/pfe/<pfe>/cm/<cm>/Host_Loopback/<cm>/HOST_LOOPBACK_MAKE_CMERROR_ID[<id>])
This issue affects Juniper Networks Junos OS:

  *  All versions earlier than 20.4R3-S8;
  *  21.1 versions earlier than 21.1R3-S4;
  *  21.2 versions earlier than 21.2R3-S6;
  *  21.3 versions earlier than 21.3R3-S3;
  *  21.4 versions earlier than 21.4R3-S5;
  *  22.1 versions earlier than 22.1R2-S2, 22.1R3;
  *  22.2 versions earlier than 22.2R2-S1, 22.2R3.

Weakness: CWE-76 (Improper Neutralization of Equivalent Special Elements)

## Which versions are affected by CVE-2024-21600?

It affects 1 product.


Products: Juniper Junos.

## How do I fix CVE-2024-21600?

No fix has been published for CVE-2024-21600 yet. Limit exposure of the affected software until one is available.

## Is CVE-2024-21600 being exploited?

There is no known exploitation of CVE-2024-21600 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-2024-21600 and fix it if it is affected.

What it is: CVE-2024-21600 is a medium-severity denial of service vulnerability in Juniper Junos, published on 12 Jan 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2024-21600 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-2024-21600/ (Markdown: https://insights.sbomify.com/CVE-2024-21600/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-21600
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-21600
- OSV: https://osv.dev/vulnerability/CVE-2024-21600

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-21600/
Summaries are generated and may contain mistakes; the official description above is the record.