Can you explain this vulnerability to me?

CVE-2026-25519 is an incorrect access control vulnerability in the OpenSlides authentication service affecting versions 4.2.5 through 4.2.28. OpenSlides supports local logins with username and password and optionally single sign-on (SSO) via SAML through an external Identity Provider (IDP). The vulnerability allows users synchronized via the external IDP to bypass proper authentication by logging in through the local login form using the OpenSlides username of a SAML user and a trivial, universal password valid for all such SAML users.

This means that an attacker can gain unauthorized access to accounts of SAML users without knowing their actual passwords, due to improper password verification logic that did not properly check for empty or missing passwords.

The issue was fixed in OpenSlides version 4.2.29 by correcting the password verification logic to ensure that users with empty or missing passwords cannot authenticate.

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How can this vulnerability impact me? :

This vulnerability can have a severe impact as it allows unauthorized users to gain access to accounts of SAML-synced users without proper credentials.

• Unauthorized access to sensitive data due to bypassing authentication.
• Potential modification or deletion of data, compromising data integrity.
• Disruption of service availability by unauthorized users.

The CVSS v3.1 base score of 8.1 reflects a high severity, indicating that exploitation can lead to significant confidentiality, integrity, and availability impacts.

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How does this vulnerability affect compliance with common standards and regulations (like GDPR, HIPAA)?:

I don't know

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How can this vulnerability be detected on my network or system? Can you suggest some commands?

[{'type': 'paragraph', 'content': 'This vulnerability involves an incorrect access control in OpenSlides authentication where SAML-synced users can log in locally using a trivial universal password. Detection would involve monitoring authentication attempts for logins of SAML users via the local login form using weak or trivial passwords.'}, {'type': 'paragraph', 'content': 'Since the vulnerability is related to authentication bypass via a trivial password for SAML users, you can detect it by checking authentication logs for unusual successful logins of SAML users with weak or default passwords.'}, {'type': 'paragraph', 'content': 'Specific commands are not provided in the resources, but general approaches include:'}, {'type': 'list_item', 'content': 'Review OpenSlides authentication logs for local login attempts of SAML users.'}, {'type': 'list_item', 'content': 'Use grep or similar tools to search logs for successful logins with known trivial passwords or empty password fields.'}, {'type': 'list_item', 'content': 'Monitor for multiple failed login attempts followed by a successful login with a trivial password.'}, {'type': 'paragraph', 'content': 'Example command to search logs (assuming logs contain username and password fields):'}, {'type': 'list_item', 'content': "grep -i 'local login' /path/to/openslides/logs | grep 'SAML_user' | grep 'password=trivial_password'"}, {'type': 'paragraph', 'content': 'However, no explicit commands or detection scripts are provided in the available resources.'}] [2, 1, 3]

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What immediate steps should I take to mitigate this vulnerability?

The primary mitigation step is to update OpenSlides to version 4.2.29 or later, where the vulnerability has been patched.

The patch corrects the password verification logic in the authentication service to prevent authentication bypass by ensuring that users must have a valid password set.

Additional steps include:

• Apply the fix from the openslides-auth-service repository if you maintain a custom deployment.
• Restrict or monitor local login access for users synchronized via SAML until the update is applied.
• Review and tighten access control policies related to authentication.

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