CVE-2021-21379 in XWiki
Summary
by MITRE • 03/13/2021
XWiki Platform is a generic wiki platform offering runtime services for applications built on top of it. In affected versions of XWiki Platform, the `{{wikimacrocontent}}` executes the content with the rights of the wiki macro author instead of the caller of that wiki macro. This makes possible to inject scripts through it and they will be executed with the rights of the wiki macro (very often a user which has Programming rights). Fortunately, no such macro exists by default in XWiki Standard but one could have been created or installed with an extension. This vulnerability has been patched in versions XWiki 12.6.3, 11.10.11 and 12.8-rc-1. There is no easy workaround other than disabling the affected macros. Inserting content in a safe way or knowing what is the user who called the wiki macro is not easy.
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Analysis
by VulDB Data Team • 04/01/2021
The CVE-2021-21379 vulnerability represents a critical privilege escalation flaw within the XWiki Platform, a widely-used generic wiki platform that provides runtime services for applications built upon it. This vulnerability stems from a fundamental flaw in how the platform handles macro execution permissions, specifically affecting the `{{wikimacrocontent}}` functionality. The issue manifests when wiki macros execute content with the privileges of the macro author rather than the user who invoked the macro, creating a significant security gap that can be exploited by malicious actors. This misconfiguration allows for arbitrary script injection through the affected macro system, potentially enabling attackers to execute code with elevated privileges typically reserved for users with programming rights.
The technical exploitation of this vulnerability occurs through the improper privilege delegation mechanism within XWiki's macro execution framework, which aligns with CWE-276 principles regarding incorrect privilege assignment. Attackers can leverage this flaw by creating or installing malicious wiki macros that contain malicious scripts, which will then execute with the elevated privileges of the macro author rather than the invoking user. This creates a dangerous scenario where even users with limited permissions can potentially gain administrative capabilities through the execution of crafted macro content. The vulnerability's impact is particularly severe because it operates at the core execution layer of the platform, bypassing normal access control mechanisms that should normally prevent such privilege escalation.
The operational implications of this vulnerability extend beyond simple code execution to encompass potential full system compromise when combined with other attack vectors. Since the affected macros can execute with programming rights, attackers who successfully exploit this vulnerability could potentially modify system configurations, access sensitive data, or establish persistent backdoors within the wiki environment. The fact that no default macro exists in XWiki Standard but custom macros could be installed through extensions means that organizations using third-party extensions or custom macro development are particularly vulnerable. This vulnerability represents a classic example of insecure privilege management as outlined in ATT&CK tactic TA0004 (Privilege Escalation), where an attacker leverages a legitimate system function to gain elevated privileges.
The patching process for this vulnerability required updates to specific versions of the XWiki Platform, with fixes released in versions 12.6.3, 11.10.11, and 12.8-rc-1, demonstrating the severity of the issue and the need for immediate remediation. Organizations affected by this vulnerability face limited mitigation options beyond disabling the affected macro functionality entirely, as the underlying architectural flaw cannot be easily worked around without significant system modifications. The complexity of implementing safe content insertion mechanisms or user identification processes highlights the fundamental nature of the security flaw, which affects the core permission model of the platform. This vulnerability underscores the critical importance of proper privilege management and access control implementation in web-based collaborative platforms where users with different permission levels interact with shared content systems.