CVE-2026-92232 in Joomla Extension
Summary
by MITRE • 09/29/2026
Joomla! Core - [20260916] - Core - XSS filter bypass in InputFilter via whitespace characters in HTML data URIs in Joomla 1.5.0-5.4.8, 6.0.0-6.1.3 - The cleanAttribute method removes HTML data URIs, however injected whitespaces characters could circumvent that cleanup, causing an XSS vector.
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Analysis
by VulDB Data Team • 09/29/2026
The vulnerability identified as CVE-20260916 represents a critical security flaw within the Joomla! content management system's core input filtering mechanisms. This issue specifically affects versions ranging from 1.5.0 through 5.4.8, and extends into the newer 6.0.0 to 6.1.3 release cycles. The root cause lies in the InputFilter component, which is responsible for sanitizing user-supplied data before it is processed or stored by the application. Specifically, the cleanAttribute method was designed to strip out potentially dangerous HTML data URIs from input fields. However, this implementation failed to account for the presence of whitespace characters embedded within these URI structures, allowing attackers to bypass the intended security controls and inject malicious scripts into web pages viewed by other users.
From a technical perspective, the flaw stems from an insufficient validation logic in the cleanAttribute function. When processing HTML attributes that contain data URIs, such as those used for embedding images or media directly within markup, the filter attempts to remove any content identified as a data URI scheme. The implementation likely relied on pattern matching or string manipulation techniques that did not normalize input by removing whitespace before evaluation. Consequently, an attacker can insert spaces, tabs, or newlines into the protocol identifier part of a data URI, for example writing data: text/html instead of data:text/html. This variation causes the regular expression or parsing logic to fail in recognizing the payload as a prohibited data URI, thereby allowing it to pass through the filter intact and be rendered by the victim's browser.
The operational impact of this vulnerability is significant due to its classification as an XSS vector. Cross-Site Scripting allows attackers to execute arbitrary JavaScript code in the context of the vulnerable website. This can lead to session hijacking, where stolen cookies or authentication tokens are transmitted to the attacker, granting unauthorized access to user accounts. It also enables defacement of web pages, redirection of users to malicious sites for phishing attacks, and potentially keylogging activities if combined with other techniques. Since this flaw exists in the core input filtering layer, it affects a wide range of components within Joomla! that rely on this sanitization process, making exploitation relatively straightforward for any user who can submit form data or modify content fields accessible via HTTP requests.
This vulnerability aligns closely with CWE-79, which defines Improper Neutralization of Input During Web Page Generation commonly known as Cross-site Scripting. The specific mechanism of bypassing filters using whitespace characters is a classic example of input normalization failure often associated with CWE-601 URL Redirection to Untrusted Site or similar parsing inconsistencies. In the context of the MITRE ATT&CK framework, this exploit maps to T1059 Command and Control via Application Layer Protocol if used for beaconing, but more directly relates to T1189 Drive-by Client Side Script Injection when executed automatically upon page load, or T1204 User Execution if it requires user interaction. The ability to bypass input filters highlights a gap in the defense-in-depth strategy employed by the application's security architecture.
Mitigation strategies for this vulnerability involve immediate patching of the Joomla! installation to the latest stable version where the InputFilter logic has been corrected to handle whitespace normalization properly. Administrators should ensure that all instances of affected software are updated, as the flaw persists across multiple major and minor release branches. In addition to updating, implementing a Web Application Firewall can provide an additional layer of protection by detecting and blocking requests containing suspicious patterns such as encoded or spaced-out data URIs before they reach the application logic. Furthermore, developers should enforce strict Content Security Policy headers that restrict the sources from which scripts can be loaded, thereby mitigating the impact even if an XSS vector is successfully injected into the page markup.