# CVE-2021-42835: Race condition in n/a

> A TOCTOU race condition in the update service allows low-privileged attackers to execute arbitrary code as SYSTEM via RPC.

- **Severity:** High 7.0 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 8 Dec 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-724p-rm8h-wjx7

## What is CVE-2021-42835?

CVE-2021-42835 is a high-severity vulnerability in n/a, published on 8 Dec 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

An issue was discovered in Plex Media Server through 1.24.4.5081-e362dc1ee. An attacker (with a foothold in a endpoint via a low-privileged user account) can access the exposed RPC service of the update service component. This RPC functionality allows the attacker to interact with the RPC functionality and execute code from a path of his choice (local, or remote via SMB) because of a TOCTOU race condition. This code execution is in the context of the Plex update service (which runs as SYSTEM).

Weakness: CWE-367 (Time-of-check Time-of-use (TOCTOU) Race Condition)

## Which versions are affected by CVE-2021-42835?

It affects 1 product.


Products: Plex Media Server.

## How do I fix CVE-2021-42835?

No fix has been published for CVE-2021-42835 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-42835 being exploited?

There is no known exploitation of CVE-2021-42835 in the wild and no public exploit code.

Public exploit code:

- Plex media server local privilige escalation poc -  CVE-2021-42835 (github_poc): https://github.com/netanelc305/PlEXcalaison

## Other vulnerabilities in n/a

- [CVE-2026-96656](https://insights.sbomify.com/CVE-2026-96656/): Plex Media Server External Control of File Name or Path (high 8.6, exploited in the wild)
- [CVE-2020-5741](https://insights.sbomify.com/CVE-2020-5741/): Plex Media Server Remote Code Execution (high 7.2, exploited in the wild)
- [CVE-2026-96654](https://insights.sbomify.com/CVE-2026-96654/): Plex Media Server Improper Neutralization of Encoded URI Schemes in a Web Page (medium 6.9, exploited in the wild)
- [CVE-2026-96652](https://insights.sbomify.com/CVE-2026-96652/): Plex Media Server Server-Side Request Forgery (SSRF) (medium 5.3, exploited in the wild)
- [CVE-2026-96655](https://insights.sbomify.com/CVE-2026-96655/): Plex Media Server Server-Side Request Forgery (SSRF) (medium 5.3, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-42835 and fix it if it is affected.

What it is: CVE-2021-42835 is a high-severity vulnerability in n/a, published on 8 Dec 2021. 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-2021-42835 in the wild and no public exploit code.

Affected product: n/a. 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-2021-42835/ (Markdown: https://insights.sbomify.com/CVE-2021-42835/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-42835
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-42835
- OSV: https://osv.dev/vulnerability/CVE-2021-42835

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-42835/
Summaries are generated and may contain mistakes; the official description above is the record.