CVE-2020-26280: XSS in OpenSlides Assembly System

The XSS vulnerability in OpenSlides allows an attacker to inject arbitrary JavaScript code into various fields where users can enter rich text, such as personal notes or motions. When other users view this text, the injected script will execute in their browser context. This can have severe consequences, including session hijacking, redirection to malicious websites, and defacement of the OpenSlides interface. Crucially, an attacker could leverage this to manipulate votes during assemblies, potentially altering the outcome of decisions. The blast radius extends to all users who view the compromised text, making it a significant risk for organizations relying on OpenSlides for assembly management. The ability to inject and execute code within a trusted application like OpenSlides mirrors the impact of other high-profile XSS vulnerabilities, highlighting the importance of robust input validation.

1. Reserved2020-10-01
2. Published2020-12-18
3. Modified2024-08-04
4. EPSS updated2026-04-02

The primary mitigation for CVE-2020-26280 is to upgrade OpenSlides to version 3.3 or later, which includes the necessary input validation fixes. If immediate upgrading is not feasible, consider implementing temporary workarounds. Web Application Firewalls (WAFs) configured to detect and block XSS payloads can provide a layer of defense. Specifically, look for rules that identify JavaScript injection attempts within rich text fields. Additionally, carefully review and sanitize all user-supplied input before displaying it within the application. After upgrading to version 3.3, verify the fix by attempting to inject a simple JavaScript payload (e.g., <script>alert('XSS')</script>) into a rich text field and confirming that it is properly sanitized and does not execute.