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CVE-2025-21638 Siemens CVE debrief

A null-pointer dereference vulnerability exists in the Linux kernel's SCTP (Stream Control Transmission Protocol) sysctl implementation for the `auth_enable` parameter. The flaw occurs when the kernel accesses `current->nsproxy` to obtain network namespace information during sysctl read/write operations. In specific scenarios—such as when a task is exiting—`current->nsproxy` can be NULL, causing an Oops (kernel crash). This was identified by syzbot using the `acct(2)` system call. The vulnerability stems from inconsistent namespace handling: using the reader's/writer's network namespace versus only the opener's namespace. The fix retrieves the `net` structure from `table->data` using `container_of()` rather than through the current task's namespace proxy. Siemens has confirmed this vulnerability affects the GNU/Linux subsystem of the SIMATIC S7-1500 TM MFP industrial control system.

Vendor
Siemens
Product
SIMATIC S7-1500 TM MFP - GNU/Linux subsystem
CVSS
HIGH 7.1
CISA KEV
Not listed in stored evidence
Original CVE published
2025-01-19
Original CVE updated
2026-07-30
Advisory published
2025-01-19
Advisory updated
2026-07-30

Who should care

Organizations running Siemens SIMATIC S7-1500 TM MFP systems with the GNU/Linux subsystem enabled, industrial control system operators, Linux kernel maintainers for embedded/ICS environments, and security teams responsible for OT/ICS infrastructure.

Technical summary

The vulnerability exists in the Linux kernel's SCTP protocol implementation, specifically in the sysctl handler for `auth_enable`. The code incorrectly uses `current->nsproxy` to access network namespace information, which can be NULL when the current task is exiting. This results in a null-pointer dereference (Oops). The proper fix uses `container_of()` on `table->data` to obtain the `net` structure directly. The vulnerability is local (AV:L), requires low privileges (PR:L), and can cause high availability impact (A:H) through denial of service (kernel crash).

Defensive priority

medium

Recommended defensive actions

  • Apply kernel updates from Siemens when available for the SIMATIC S7-1500 TM MFP GNU/Linux subsystem
  • Restrict interactive shell access to the GNU/Linux subsystem to trusted personnel only
  • Only build and run applications from trusted sources on affected systems
  • Monitor for kernel Oops messages in system logs that may indicate exploitation attempts
  • Review network namespace isolation configurations to minimize attack surface

Evidence notes

The vulnerability description indicates this was resolved in the Linux kernel with a commit that avoids using `current->nsproxy` in the SCTP sysctl `auth_enable` handler. The issue was detected by syzbot using `acct(2)`. Siemens has included this CVE in their security advisory SSA-265688 for the SIMATIC S7-1500 TM MFP product, with the CISA ICS advisory ICSA-24-102-01 tracking this and related vulnerabilities. The advisory was initially published on 2024-04-09 and has been updated multiple times through September 2025 to include additional CVEs.

Sources and references

Verified primary and authoritative sources

  • CVE-2025-21638 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2025-21638

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2025-21638 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2025-21638

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

  • Source item URL

    Unverified legacy reference

    URL: https://raw.githubusercontent.com/cisagov/CSAF/develop/csaf_files/OT/white/2024/icsa-24-102-01.json

    cisa_csaf

  • Source reference

    Unverified legacy reference

    URL: https://cert-portal.siemens.com/productcert/csaf/ssa-265688.json

    Reference

  • Source reference

    Unverified legacy reference

    URL: https://cert-portal.siemens.com/productcert/html/ssa-265688.html

    Reference

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/news-events/ics-advisories/icsa-24-102-01

    Reference

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/news-events/ics-alerts/ics-alert-10-301-01

    Reference

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/resources-tools/resources/ics-recommended-practices

    Reference

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/topics/industrial-control-systems

    Reference

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/sites/default/files/recommended_practices/NCCIC_ICS-CERT_Defense_in_Depth_2016_S508C.pdf

    Reference

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.