CVE-2025-40186 remediation guide

Linux

In the Linux kernel, the following vulnerability has been resolved: tcp: Don't call reqsk_fastopen_remove() in tcp_conn_request(). syzbot reported the splat below in tcp_conn_request(). [0] If a listener is close()d while a TFO socket is being processed in tcp_conn_request(), inet_csk_reqsk_queue_add() does not set reqsk->sk and calls inet_child_forget(), which calls tcp_disconnect() for the TFO socket. After the cited commit, tcp_disconnect() calls reqsk_fastopen_remove(), where reqsk_put() is called due to !reqsk->sk. Then, reqsk_fastopen_remove() in tcp_conn_request() decrements the last...

Open CVE record

Research in progress

A verified fixed-version field is not available. Use the linked NVD and supporting references, then confirm the vendor-supported path before changing production systems.

ProductLinux

Affected versions>= 7ec092a91ff351dcde89c23e795b73a328274db6 < e359b742eac1eac75cff4e38ee2e8cea492acd9b, >= a4378dedd6e07e62f2fccb17d78c9665718763d0 < ff6a8883f96a5bc74241ce5b3d431a6dcfa2124d, >= 33a4fdf0b4a25f8ce65380c3b0136b407ca57609 < eb85ad5f23268d64b037bfb545cbcba3752f90c7, >= 17d699727577814198d744d6afe54735c6b54c99 < 643a94b0cf767325e953591c212be2eb826b9d7f, >= dfd06131107e7b699ef1e2a24ed2f7d17c917753 < 422c1c173c39bbbae1e0eaaf8aefe40b2596233b, >= fa4749c065644af4db496b338452a69a3e5147d9 < c11ace909e873118295e9eb22dc8c58b0b50eb32, >= 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01 < 64dc47a13aa3d9daf7cec29b44dca8e22a6aea15, >= 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01 < 2e7cbbbe3d61c63606994b7ff73c72537afe2e1c, >= ae313d14b45eca7a6bb29cb9bf396d977e7d28fb, >= 5.4.300 < 5.4.301, >= 5.10.245 < 5.10.246, >= 5.15.194 < 5.15.195, >= 6.1.154 < 6.1.157, >= 6.6.108 < 6.6.113, >= 6.12.49 < 6.12.54, >= 6.16.9 < 6.17, >= 6.17

Fixed versionsNo verified fixed-version field is available yet

Priority basisReview · CVSS 8.1 · EPSS 0.53%

Identify the affected asset

Confirm whether Linux is installed, record the deployed version and installation path, and identify exposed interfaces.

Record the product name, package or appliance identifier, and installed version.
Identify internet-facing, administrative, API, and internal access paths.
Preserve the pre-change configuration and relevant service logs.

Validate the affected-version match

Compare the deployed version with the affected range: >= 7ec092a91ff351dcde89c23e795b73a328274db6 < e359b742eac1eac75cff4e38ee2e8cea492acd9b, >= a4378dedd6e07e62f2fccb17d78c9665718763d0 < ff6a8883f96a5bc74241ce5b3d431a6dcfa2124d, >= 33a4fdf0b4a25f8ce65380c3b0136b407ca57609 < eb85ad5f23268d64b037bfb545cbcba3752f90c7, >= 17d699727577814198d744d6afe54735c6b54c99 < 643a94b0cf767325e953591c212be2eb826b9d7f, >= dfd06131107e7b699ef1e2a24ed2f7d17c917753 < 422c1c173c39bbbae1e0eaaf8aefe40b2596233b, >= fa4749c065644af4db496b338452a69a3e5147d9 < c11ace909e873118295e9eb22dc8c58b0b50eb32, >= 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01 < 64dc47a13aa3d9daf7cec29b44dca8e22a6aea15, >= 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01 < 2e7cbbbe3d61c63606994b7ff73c72537afe2e1c, >= ae313d14b45eca7a6bb29cb9bf396d977e7d28fb, >= 5.4.300 < 5.4.301, >= 5.10.245 < 5.10.246, >= 5.15.194 < 5.15.195, >= 6.1.154 < 6.1.157, >= 6.6.108 < 6.6.113, >= 6.12.49 < 6.12.54, >= 6.16.9 < 6.17, >= 6.17. Treat incomplete inventory results as unresolved.

Prioritize with independent signals

The CVSS severity warrants an early asset and exposure review. Combine this signal with asset criticality, exposure, compensating controls, and business impact.

Apply supported remediation

Follow the vendor advisory or supported update path. Current fixed-version status: No verified fixed-version field is available yet. Preserve configuration and rollback material before change.

Verify the result

Confirm the resulting version, service health, authentication and access paths, monitoring coverage, and relevant security logs.

Confirm the expected version and package state.
Run a functional health check for critical service paths.
Review authentication, error, application, and security monitoring logs.
Reassess exposure if the supported fix cannot be applied.

Operational boundary

This page does not replace the vendor advisory, support contract, change-management process, or recovery plan. Do not infer that an asset is unaffected from an incomplete inventory query or a missing fixed-version field.