CVE-2026-100240 in MediaWiki
Summary
by MITRE • 09/29/2026
Missing Authorization vulnerability in Wikimedia Foundation Mediawiki - TemplateSandbox Extension allows Accessing Functionality Not Properly Constrained by ACLs.
This issue affects Mediawiki - TemplateSandbox Extension: from * before 1.46.1, 1.45.5, 1.43.10.
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Analysis
by VulDB Data Team • 09/29/2026
The Wikimedia Foundation's MediaWiki platform, specifically within the TemplateSandbox extension prior to versions 1.46.1, 1.45.5, and 1.43.10, contains a critical access control flaw that permits unauthorized users to execute functionality intended for privileged accounts or restricted contexts. This vulnerability stems from an insufficient enforcement of Access Control Lists (ACLs) within the extension's core logic, allowing attackers who possess only basic wiki editing privileges—or in some configurations, no authentication at all—to bypass standard permission checks. The TemplateSandbox is designed primarily as a debugging and testing tool for developers to preview template expansions without permanently modifying pages; however, its implementation failed to adequately restrict access based on the user's role or group membership, creating a significant security gap that undermines the integrity of the wiki environment.
From a technical perspective, this issue represents a classic case of Broken Access Control, categorized under CWE-269 in the Common Weakness Enumeration standards. The flaw arises because the extension does not properly validate whether the requesting user has the necessary permissions to invoke specific functions or access sensitive data structures associated with template processing. In many MediaWiki setups, certain actions require administrative rights or special group memberships such as sysop or bureaucrat roles. When these checks are missing or incorrectly implemented within the TemplateSandbox module, an attacker can craft malicious requests that exploit this oversight. By manipulating parameters passed to the extension's API or interface endpoints, a low-privileged user can trigger operations that should be restricted, potentially leading to information disclosure, unauthorized modification of system state, or further exploitation vectors depending on how the sandboxed environment interacts with other wiki components.
The operational impact of this vulnerability is substantial for any MediaWiki instance relying on accurate access control policies. Attackers can leverage this flaw to escalate their privileges effectively within the application layer, gaining capabilities that exceed what was granted by site administrators. This could include viewing sensitive configuration details, manipulating template data in ways that affect page rendering for other users, or potentially executing server-side code if combined with other vulnerabilities such as injection flaws. For high-traffic wikis like those hosted on Wikimedia sites, the ability to bypass ACLs compromises the trust model of the platform and exposes it to abuse by malicious actors seeking to deface content, steal data, or disrupt service availability through resource exhaustion attacks facilitated by unrestricted access to expensive template processing routines.
To mitigate this risk, administrators must immediately upgrade MediaWiki and its extensions to patched versions 1.46.1, 1.45.5, or 1.43.10, depending on their current deployment branch. These releases contain the necessary code corrections that enforce strict authorization checks before allowing access to TemplateSandbox functionality. Additionally, organizations should review their server-side logging and monitoring systems for signs of exploitation attempts targeting this specific extension path. Implementing a Web Application Firewall (WAF) with rules tailored to detect anomalous requests related to template sandbox parameters can provide an additional layer of defense during the transition period. Furthermore, adhering to the principle of least privilege by ensuring that only trusted developers have access to debugging tools in production environments remains a best practice recommended by industry frameworks such as MITRE ATT&CK under techniques involving unauthorized resource access and potential lateral movement within web application architectures.