# CVE-2023-36841: Junos OS: MX Series: Receipt of malformed TCP traffic will cause a Denial of Service

> Unauthenticated attackers can cause a denial of service on Juniper MX routers by sending malformed TCP traffic to interfaces configured with PPPoE and tcp-mss.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/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:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 12 Oct 2023
- **Updated:** 18 Sep 2024
- **Also known as:** GHSA-j5xw-gh42-g53c

## What is CVE-2023-36841?

CVE-2023-36841 is a high-severity denial of service vulnerability in Juniper Junos, published on 12 Oct 2023. 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 MX Series allows a unauthenticated network-based attacker to cause an infinite loop, resulting in a Denial of Service (DoS).

An attacker who sends malformed TCP traffic via an interface configured with PPPoE, causes an infinite loop on the respective PFE. This results in consuming all resources and a manual restart is needed to recover.

This issue affects interfaces with PPPoE configured and tcp-mss enabled.

This issue affects Juniper Networks Junos OS

  *  All versions prior to 20.4R3-S7;
  *  21.1 version 21.1R1 and later versions;
  *  21.2 versions prior to 21.2R3-S6;
  *  21.3 versions prior to 21.3R3-S5;
  *  21.4 versions prior to 21.4R3-S3;
  *  22.1 versions prior to 22.1R3-S4;
  *  22.2 versions prior to 22.2R3;
  *  22.3 versions prior to 22.3R2-S2;
  *  22.4 versions prior to 22.4R2;

Weakness: CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2023-36841?

It affects 1 product.


Products: Juniper Junos.

## How do I fix CVE-2023-36841?

No fix has been published for CVE-2023-36841 yet. Limit exposure of the affected software until one is available.

## Is CVE-2023-36841 being exploited?

There is no known exploitation of CVE-2023-36841 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-2023-36841 and fix it if it is affected.

What it is: CVE-2023-36841 is a high-severity denial of service vulnerability in Juniper Junos, published on 12 Oct 2023. 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-2023-36841 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-2023-36841/ (Markdown: https://insights.sbomify.com/CVE-2023-36841/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-36841
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-36841
- OSV: https://osv.dev/vulnerability/CVE-2023-36841

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-36841/
Summaries are generated and may contain mistakes; the official description above is the record.