PatchSiren

PatchSiren cyber security CVE debrief

CVE-2025-21666 Siemens CVE debrief

A null pointer dereference vulnerability exists in the Linux kernel's vsock (virtual socket) subsystem, specifically within the vsock_has_data and vsock_has_space functions. This flaw can be triggered when these functions are called without proper validation of the underlying socket transport state, leading to a kernel crash and denial of service. The vulnerability affects the GNU/Linux subsystem embedded in Siemens SIMATIC S7-1500 TM MFP industrial control devices. Local attackers with low privileges can exploit this to cause system instability. No patch is currently available from the vendor.

Vendor
Siemens
Product
SIMATIC S7-1500 TM MFP - GNU/Linux subsystem
CVSS
MEDIUM 5.5
CISA KEV
Not listed in stored evidence
Original CVE published
2024-04-09
Original CVE updated
2026-05-14
Advisory published
2024-04-09
Advisory updated
2026-05-14

Who should care

Industrial control system operators using Siemens SIMATIC S7-1500 TM MFP with the GNU/Linux subsystem enabled; OT security teams managing embedded Linux environments; infrastructure owners relying on continuous availability of PLC-based automation systems.

Technical summary

The vulnerability resides in the Linux kernel's virtual socket (vsock) implementation. The vsock_has_data and vsock_has_space functions fail to validate whether the socket's transport pointer is non-null before dereferencing it. This can occur during certain socket state transitions or when the transport layer has not been fully initialized. Exploitation requires local access with low privileges and results in a kernel oops/panic, causing denial of service. The CVSS 3.1 score of 5.5 (MEDIUM) reflects the local attack vector and high availability impact with no confidentiality or integrity effects.

Defensive priority

medium

Recommended defensive actions

  • Restrict interactive shell access to the GNU/Linux subsystem to trusted personnel only
  • Implement application whitelisting to ensure only trusted applications are built and executed
  • Monitor for anomalous process behavior or unexpected kernel panics on affected devices
  • Apply defense-in-depth strategies per CISA ICS recommended practices pending vendor patch availability
  • Subscribe to Siemens ProductCERT notifications for firmware updates addressing this vulnerability

Evidence notes

CVE published 2024-04-09; CISA ICS advisory ICSA-24-102-01 tracks this vulnerability with multiple revision updates through 2025-09-09. Siemens CSAF advisory SSA-265688 provides product-specific guidance. CVSS 3.1 vector confirms local attack vector with low attack complexity.

Sources and references

Verified primary and authoritative sources

  • CVE-2025-21666 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2025-21666

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

  • CVE-2025-21666 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2025-21666

    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.