OpenSlides, a web-based presentation and assembly system, contains an authentication bypass vulnerability in versions prior to 4.2.29. The vulnerability affects users synced from external SAML identity providers, allowing attackers to bypass authentication by using the SAML username with a trivial password that works for all SAML users. This represents a critical access control flaw that could allow unauthorized access to user accounts. The issue has been patched in version 4.2.29.