CVE-2025-21848 Siemens CVE debrief

Who should care

Siemens SIMATIC S7-1500 operators and integrators, especially anyone running the listed CPU models in production or using the additional GNU/Linux subsystem and its shell access.

Technical summary

The supplied description says the kernel fix adds a missing return-value check for nfp_app_ctrl_msg_alloc() inside nfp_bpf_cmsg_alloc() to prevent a null pointer dereference. The CISA-republished Siemens CSAF advisory (ICSA-25-162-05 / SSA-082556) lists five affected SIMATIC S7-1500 CPU product variants and gives CVSS v3.1 AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H, indicating a local, low-privilege condition with high availability impact. The advisory also states that no fix is currently available.

Defensive priority

Medium overall, but treat as time-sensitive for affected production CPUs because the advisory lists no fix and only mitigation guidance.

Recommended defensive actions

• Identify whether any of the five listed Siemens SIMATIC S7-1500 CPU variants are deployed in your environment.
• Restrict access to the interactive shell of the additional GNU/Linux subsystem to trusted personnel only.
• Only build and run applications from trusted sources on affected systems.
• Apply Siemens and CISA defense-in-depth guidance and segment affected industrial control assets where possible.
• Monitor Siemens ProductCERT and CISA advisory updates for a future fix or revised mitigation guidance.

Evidence notes

Grounded in the supplied CISA CSAF source ICSA-25-162-05 (SSA-082556), initially published 2025-06-10 and last updated 2026-05-14. The advisory lists five affected Siemens products, states 'Currently no fix is available,' and includes mitigations limiting shell access and trusting application sources. The description explicitly ties the issue to a missing return-value check for nfp_app_ctrl_msg_alloc() in nfp_bpf_cmsg_alloc() to prevent a null pointer dereference. The provided CVSS vector is CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H. No KEV listing is indicated in the supplied enrichment.

Official resources