CVE-2026-25789 - Firmware Update Page Filename Sanitization Vulnerability

CVE-2026-25789 exposes a vulnerability affecting certain devices where the Firmware Update page lacks proper filename validation and sanitization. A remote attacker could exploit this by crafting a malicious filename containing JavaScript code and socially engineering a user into selecting this “firmware” file for upload. The malicious JavaScript would then execute within the context of the authenticated user’s session, even without the file being fully uploaded, potentially allowing the attacker to hijack the user’s session or steal their credentials. This vulnerability highlights the importance of proper input validation to prevent cross-site scripting (XSS) attacks. Siemens AG has acknowledged this vulnerability.

Attack Chain

1. Attacker identifies a vulnerable device with a Firmware Update page.
2. Attacker crafts a malicious filename containing embedded JavaScript code (e.g., <script>alert("XSS")</script>.bin).
3. Attacker hosts or distributes the malicious “firmware” file.
4. Attacker uses social engineering to trick a user into selecting the malicious file on the Firmware Update page.
5. The user selects the malicious file for upload through the web interface.
6. The vulnerable device processes the filename without proper sanitization.
7. The embedded JavaScript code is executed in the user’s browser session.
8. Attacker gains control of the user’s session, enabling credential theft or other malicious activities.

Impact

Successful exploitation of CVE-2026-25789 can lead to session hijacking and credential theft. An attacker could gain unauthorized access to the device’s management interface, potentially modifying device configurations, injecting malware, or accessing sensitive data. While the NVD entry does not specify the number of affected devices, it is classified as HIGH severity with a CVSS v3.1 score of 7.1.

Recommendation

• Examine web server logs for requests to the Firmware Update page containing suspicious filenames with JavaScript-related keywords using the Sigma rule “Detect Suspicious Firmware Update Filenames”.
• Implement input validation and sanitization on the Firmware Update page to prevent the execution of arbitrary JavaScript code.
• Educate users about the risks of downloading and uploading firmware files from untrusted sources.
• Apply the security patch provided by Siemens AG to remediate CVE-2026-25789 (reference: https://cert-portal.siemens.com/productcert/html/ssa-688146.html).