ICSA-26-134-15: Siemens SIMATIC S7 PLC Web Server

CISA's summary

Summary: SIMATIC S7 PLCs contain multiple vulnerabilities in the web server that could allow an attacker to perform cross-site scripting attacks. Siemens has released new versions for several affected products and recommends to update to the latest versions. Siemens is preparing further fix versions and recommends specific countermeasures for products where fixes are not, or not yet available.

Products, as the advisory lists them

DeSpy has not checked any unit, hardware revision or firmware.

Vulnerabilities in this advisory

• CVE-2026-25786 — CVE-2026-25786 · CWE-79

  Affected devices do not properly validate and sanitize PLC/station name rendered on the "communication" parameters page of the web interface. This could allow an authenticated attacker who is authorized to download a TIA project into the product, to inject malicious scripts into the page. If a benign user with appropriate rights accesses the "communication" parameters page, the malicious code would be executed in the scope of their web session.

• CVE-2026-25787 — CVE-2026-25787 · CWE-79

  Affected devices do not properly validate and sanitize Technology Object (TO) name rendered on the "Motion Control Diagnostics" page of the web interface. This could allow an authenticated attacker who is authorized to download a TIA project into the product, to inject malicious scripts into the page. If a benign user with appropriate rights accesses the "Motion Control Diagnostics" parameters page, the malicious code would be executed in the scope of their web session.

• CVE-2026-25789 — CVE-2026-25789 · CWE-79

  Affected devices do not properly validate and sanitize filenames on the Firmware Update page. This could allow a remote attacker to social engineer the user into selecting the modified firmware file to be uploaded. This would result in malitcious JavaScript execution in the context of the authenticated user's session without requiring the file to be uploaded, potentially leading to session hijacking or credential theft.

Acknowledgments, as the advisory lists them

• Siemens ProductCERT: reported these vulnerabilities to CISA.
• Lukas Sohrmann: reported these vulnerabilities to Siemens

The advisory's legal notice

The use of Siemens Security Advisories is subject to the terms and conditions listed on: https://www.siemens.com/productcert/terms-of-use.

Sources

• The advisory at cisa.gov
• The CSAF document (JSON)

DeSpy's copy of this version is dated 2026-09-28.