CVE-2026-52766 in YesWiki
Summary
by MITRE • 09/05/2026
YesWiki is a wiki system written in PHP. Prior to version 4.6.6, the {{erasespamedcomments}} wiki action (actions/EraseSpamedCommentsAction.php) accepts a suppr[] array from POST and deletes every wiki page whose tag appears in that array, with no authorization check anywhere in the action body or in the page-deletion path it invokes. Combined with YesWiki's allow-by-default action ACL model, any user who has page write access, which is the default for everyone (default_write_acl='*') on a fresh install can permanently delete arbitrary wiki pages, including the front page, admin pages, and pages owned by other users. This issue has been patched in version 4.6.6.
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Analysis
by VulDB Data Team • 09/05/2026
YesWiki is an open-source wiki system developed in PHP that allows for collaborative content creation and management. A critical security vulnerability was identified within versions prior to 4.6.6, specifically affecting the erasespamedcomments action located in actions/EraseSpamedCommentsAction.php. This functionality is designed to remove comments flagged as spam by iterating through a provided array of tags associated with those comments. However, the implementation contains a severe authorization flaw that allows for unauthorized data destruction. The core technical issue lies in the fact that this action accepts an input parameter named suppr[] via HTTP POST requests without performing any authentication or access control checks within the action body itself. Furthermore, the underlying page deletion mechanism invoked by this action also lacks independent verification of user permissions relative to the specific pages being targeted.
The operational impact of this vulnerability is severe due to YesWiki's default configuration settings. The system employs an allow-by-default Access Control List model where the global setting for write access, known as default_write_acl, is set to asterisk by default on fresh installations. This configuration effectively grants every user who can access the wiki interface full write permissions across all pages unless explicitly restricted by administrators. Consequently, any authenticated or even unauthenticated user depending on server configuration can exploit this flaw to permanently delete arbitrary wiki content. The attacker does not need elevated privileges because the vulnerability bypasses standard permission checks entirely. This means that critical infrastructure such as administrative pages, system configurations, and personal data owned by other users are all at risk of being erased without consent or audit trail integrity.
This vulnerability aligns with CWE-862 Missing Authorization, where a software application fails to enforce proper access controls before allowing an action to proceed. Additionally, the exploitation technique maps to MITRE ATT&CK techniques related to Data Destruction and potentially Privilege Escalation if combined with other vectors to gain initial access. The lack of input validation on the suppr[] array further compounds the risk by enabling mass deletion operations rather than isolated incidents. Attackers can craft POST requests containing multiple tags corresponding to various pages, resulting in widespread data loss that may disrupt service availability and compromise organizational integrity.
Mitigation strategies primarily involve upgrading to version 4.6.6 or later where this issue has been patched with proper authorization checks integrated into the deletion path. For environments unable to upgrade immediately, administrators should modify the default_write_acl setting to restrict write permissions to specific user groups rather than allowing universal access. Implementing strict input validation on all POST parameters and ensuring that sensitive actions require explicit administrative privileges are also recommended defensive measures. Regular audits of action scripts for missing security controls can prevent similar vulnerabilities from being introduced in future updates or custom extensions.