CVE-2026-90917 in Joomla
Summary
by MITRE • 09/29/2026
Joomla! Core - [20260907] - Core - Improper ACL checks in outputs for tagged items in Joomla 4.0.0-5.4.8, 6.0.0-6.1.3 - An improper access check allows unauthorized users to view content items from inaccessible categories.
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Analysis
by VulDB Data Team • 09/29/2026
The vulnerability identified as CVE-20260907 represents a critical failure in the Access Control List (ACL) enforcement mechanisms within the Joomla! Content Management System, specifically affecting versions 4.0.0 through 5.4.8 and 6.0.0 through 6.1.3. This flaw is rooted in how the core application handles output generation for tagged items rather than during the initial data retrieval or permission validation phase. In a properly secured system, access checks must be performed at multiple layers to ensure that even if an attacker bypasses one layer of security, subsequent layers will still enforce restrictions based on user roles and category permissions. However, in this instance, the logic governing the display of content items associated with specific tags fails to re-validate whether the currently authenticated or anonymous user possesses the necessary read access rights for the underlying categories containing those items.
From a technical perspective, the issue stems from an improper ACL check during the rendering phase of tagged item lists. When Joomla! generates output for articles that have been assigned certain tags, it aggregates data based on tag associations without sufficiently verifying if the requesting user has permission to view each individual article's parent category. This architectural oversight allows an attacker who knows or can discover valid tag identifiers to query the system and retrieve metadata, titles, summaries, or even full content of restricted articles. The vulnerability effectively decouples the visibility of tagged items from their actual access control settings, creating a blind spot in the security perimeter that relies solely on frontend filtering rather than backend authorization enforcement.
The operational impact of this vulnerability is significant for any Joomla! deployment where sensitive information is stored within categories configured to restrict public or unauthorized user access. Attackers can exploit this flaw to perform unauthorized data disclosure, potentially exposing confidential business documents, personal identifiable information, or proprietary content that was intended to be hidden from the general public and lower-privileged users. This aligns with CWE-284 Improper Access Control, as the system fails to restrict resources to authorized actors, and also maps to MITRE ATT&CK technique T1005 Data from Local System Retrieval, where an adversary gathers data directly from local systems without executing malicious code or exploiting buffer overflows. The ability to enumerate restricted content undermines the confidentiality guarantees provided by the CMS's role-based access control model.
Mitigation for this vulnerability requires immediate action by system administrators and developers. For users running affected versions, upgrading to a patched release that corrects the ACL validation logic in the output generation module is the primary remediation strategy. Until an official patch is available or applied, administrators should consider implementing web application firewall rules that monitor for unusual patterns of tag-based queries from unauthenticated sources, although this is only a partial mitigation as it does not address the root cause within the application code. Furthermore, developers reviewing custom modules or plugins that interact with tagged items must ensure they explicitly validate access permissions against the underlying category ACLs before rendering any data to the end user, adhering to the principle of defense in depth by performing checks at both the database query level and the presentation layer.