CVE-2025-39955 remediation guide

Linux Linux, SIMATIC S7-1500 CPU 1518-4 PN/DP MFP, SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP

In the Linux kernel, the following vulnerability has been resolved: tcp: Clear tcp_sk(sk)->fastopen_rsk in tcp_disconnect(). syzbot reported the splat below where a socket had tcp_sk(sk)->fastopen_rsk in the TCP_ESTABLISHED state. [0] syzbot reused the server-side TCP Fast Open socket as a new client before the TFO socket completes 3WHS: 1. accept() 2. connect(AF_UNSPEC) 3. connect() to another destination As of accept(), sk->sk_state is TCP_SYN_RECV, and tcp_disconnect() changes it to TCP_CLOSE and makes connect() possible, which restarts timers. Since tcp_disconnect() forgot to clear tcp_...

Open CVE record

ProductLinux Linux, SIMATIC S7-1500 CPU 1518-4 PN/DP MFP, SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP

Affected versions>= 8336886f786fdacbc19b719c1f7ea91eb70706d4 < 7ec092a91ff351dcde89c23e795b73a328274db6, >= 8336886f786fdacbc19b719c1f7ea91eb70706d4 < a4378dedd6e07e62f2fccb17d78c9665718763d0, >= 8336886f786fdacbc19b719c1f7ea91eb70706d4 < 33a4fdf0b4a25f8ce65380c3b0136b407ca57609, >= 8336886f786fdacbc19b719c1f7ea91eb70706d4 < 17d699727577814198d744d6afe54735c6b54c99, >= 8336886f786fdacbc19b719c1f7ea91eb70706d4 < dfd06131107e7b699ef1e2a24ed2f7d17c917753, >= 8336886f786fdacbc19b719c1f7ea91eb70706d4 < fa4749c065644af4db496b338452a69a3e5147d9, >= 8336886f786fdacbc19b719c1f7ea91eb70706d4 < ae313d14b45eca7a6bb29cb9bf396d977e7d28fb, >= 8336886f786fdacbc19b719c1f7ea91eb70706d4 < 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01, >= 3.7, >= V3.1.6, >= 3.7 < 5.4.300, >= 5.5 < 5.10.245, >= 5.11 < 5.15.194, >= 5.16 < 6.1.154, >= 6.2 < 6.6.108, >= 6.7 < 6.12.49, >= 6.13 < 6.16.9, 6.17

Fixed versions5.4.300, 5.10.245, 5.15.194, 6.1.154, 6.6.108, 6.12.49, 6.16.9

Priority basisReview · CVSS 7.8 · EPSS 0.15%

Identify the affected asset

Confirm whether Linux Linux, SIMATIC S7-1500 CPU 1518-4 PN/DP MFP, SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP 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: >= 8336886f786fdacbc19b719c1f7ea91eb70706d4 < 7ec092a91ff351dcde89c23e795b73a328274db6, >= 8336886f786fdacbc19b719c1f7ea91eb70706d4 < a4378dedd6e07e62f2fccb17d78c9665718763d0, >= 8336886f786fdacbc19b719c1f7ea91eb70706d4 < 33a4fdf0b4a25f8ce65380c3b0136b407ca57609, >= 8336886f786fdacbc19b719c1f7ea91eb70706d4 < 17d699727577814198d744d6afe54735c6b54c99, >= 8336886f786fdacbc19b719c1f7ea91eb70706d4 < dfd06131107e7b699ef1e2a24ed2f7d17c917753, >= 8336886f786fdacbc19b719c1f7ea91eb70706d4 < fa4749c065644af4db496b338452a69a3e5147d9, >= 8336886f786fdacbc19b719c1f7ea91eb70706d4 < ae313d14b45eca7a6bb29cb9bf396d977e7d28fb, >= 8336886f786fdacbc19b719c1f7ea91eb70706d4 < 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01, >= 3.7, >= V3.1.6, >= 3.7 < 5.4.300, >= 5.5 < 5.10.245, >= 5.11 < 5.15.194, >= 5.16 < 6.1.154, >= 6.2 < 6.6.108, >= 6.7 < 6.12.49, >= 6.13 < 6.16.9, 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: 5.4.300, 5.10.245, 5.15.194, 6.1.154, 6.6.108, 6.12.49, 6.16.9. 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.