CVE-2026-22659 in FlaskBB
Summary
by MITRE • 07/10/2026
FlaskBB through 2.2.0, fixed in commit acc88cf, contains an authorization bypass vulnerability that allows authenticated moderators to perform unauthorized actions on topics in forums they do not control by submitting crafted topic ID lists. Attackers can include a low-ID topic from a permitted forum as an anchor in a batch request, causing the permission check applied only to the first result to pass, and then execute lock, unlock, delete, or hide actions against topics in unmoderated forums.
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Analysis
by VulDB Data Team • 07/10/2026
This vulnerability exists within FlaskBB version 2.2.0 and earlier, representing a critical authorization bypass flaw that undermines the application's access control mechanisms. The issue stems from how the software handles batch operations involving topic IDs, where permission validation is inconsistently applied across multiple requests. When an authenticated moderator submits a list of topic IDs for batch actions such as locking, unlocking, deleting, or hiding topics, the system performs permission checks only against the first topic in the submitted list. This design flaw creates a window where attackers can manipulate the request structure to include a legitimate topic from a forum they control as an anchor point, thereby passing the initial permission verification while executing unauthorized operations on topics within forums they do not moderate.
The technical implementation of this vulnerability exploits the flawed batch processing logic that assumes the first topic in a multi-topic request represents the complete scope of permissions required for all subsequent operations. This approach violates fundamental security principles of least privilege and proper access control validation, as demonstrated by the CWE-285 identifier which addresses improper authorization within software systems. The vulnerability specifically enables attackers to bypass forum-level access controls by leveraging the single-point permission check mechanism that operates on batched topic ID submissions.
From an operational perspective, this authorization bypass poses significant risks to forum administrators and users alike, as it allows malicious moderators to perform destructive actions across multiple forums without proper authorization. The impact extends beyond simple data manipulation to include potential data loss, content tampering, and disruption of community discussions. Attackers could systematically target sensitive or high-profile topics in unmoderated forums, potentially leading to information disclosure or reputational damage for forum administrators who rely on the software's access controls to maintain community integrity.
The mitigation strategy involves implementing proper batch validation where each individual topic ID undergoes independent permission verification rather than relying on a single anchor point. This approach aligns with the ATT&CK framework's privilege escalation techniques by addressing the root cause of unauthorized access through insufficient authorization checks. Security patches should enforce comprehensive authorization validation for all topics in a batch request, ensuring that each operation is validated against the appropriate forum permissions before execution. Additionally, implementing rate limiting and audit logging for batch operations can help detect suspicious activity patterns while maintaining proper operational security monitoring.
The vulnerability demonstrates how seemingly minor implementation details in access control systems can create significant security weaknesses. Organizations using FlaskBB should immediately apply the patch referenced in commit acc88cf to address this authorization bypass issue. Regular security assessments of batch processing functions and access control mechanisms should be conducted to prevent similar vulnerabilities from emerging in other parts of the application. The flaw also underscores the importance of defensive programming practices where every user action is independently validated against appropriate permission scopes rather than making assumptions based on request structure or ordering.