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CVE-2025-40800 Siemens CVE debrief

CVE-2025-40800 affects Siemens COMOS, where the IAM client does not validate the server certificate when establishing TLS connections to the authorization server. That weakness can let an attacker in the network path perform a man-in-the-middle attack against authentication traffic. CISA’s CSAF republication identifies affected COMOS product lines and points to Siemens’ remediation: update to V10.6.1 or later.

Vendor
Siemens
Product
COMOS V10.4
CVSS
CRITICAL 9.1
CISA KEV
Not listed in stored evidence
Original CVE published
2025-12-09
Original CVE updated
2026-09-30
Advisory published
2025-12-09
Advisory updated
2026-09-30

Who should care

Siemens COMOS administrators, OT/industrial system owners, and teams responsible for IAM, certificate trust, and TLS-protected authorization flows in affected environments.

Technical summary

The advisory describes a server-certificate validation failure in the IAM client during TLS setup to the authorization server. Because the client does not properly authenticate the server certificate, a network attacker can intercept or alter the TLS session and potentially influence authentication exchanges. The supplied CVSS vector is CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N, rated 7.4 High.

Defensive priority

High. Prioritize remediation on any affected COMOS deployment because the issue undermines TLS trust on an authorization path and can expose confidentiality and integrity of authentication-related traffic.

Recommended defensive actions

  • Update Siemens COMOS to V10.6.1 or later, as specified in the advisory.
  • Inventory COMOS installations and confirm whether any affected product lines listed in the advisory are deployed.
  • Treat the authorization-server TLS path as a priority remediation target and reduce unnecessary network exposure around that communication channel.
  • Apply CISA ICS recommended practices and defense-in-depth guidance while remediation is underway.

Evidence notes

The source corpus is CISA CSAF advisory ICSA-26-043-03, which republishes Siemens ProductCERT SSA-212953. The advisory description explicitly states that the IAM client is missing server certificate validation while establishing TLS connections to the authorization server, and the remediation entry directs administrators to update to V10.6.1 or later. The supplied metadata lists COMOS V10.4, V10.4.5, V10.5, and V10.6 among the affected product names.

Sources and references

Verified primary and authoritative sources

  • CVE-2025-40800 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2025-40800

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

  • CVE-2025-40800 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2025-40800

    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/2026/icsa-26-043-03.json

    cisa_csaf

  • Source reference

    Unverified legacy reference

    URL: https://cert-portal.siemens.com/productcert/csaf/ssa-212953.json

    Reference

  • Source reference

    Unverified legacy reference

    URL: https://cert-portal.siemens.com/productcert/html/ssa-212953.html

    Reference

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/news-events/ics-advisories/icsa-26-043-03

    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.