CVE-2015-5956 in TYPO3
Summary
by MITRE
The sanitizeLocalUrl function in TYPO3 6.x before 6.2.15, 7.x before 7.4.0, 4.5.40, and earlier allows remote authenticated users to bypass the XSS filter and conduct cross-site scripting (XSS) attacks via a base64 encoded data URI, as demonstrated by the (1) returnUrl parameter to show_rechis.php and the (2) redirect_url parameter to index.php.
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Analysis
by VulDB Data Team • 06/15/2022
The vulnerability identified as CVE-2015-5956 represents a critical cross-site scripting weakness in the TYPO3 content management system affecting multiple version branches including 6.x prior to 6.2.15, 7.x prior to 7.4.0, and 4.5.40 and earlier. This flaw resides within the sanitizeLocalUrl function which is responsible for validating and sanitizing URL parameters to prevent malicious input from being executed in web browsers. The vulnerability specifically exploits the insufficient filtering of base64 encoded data URIs that can bypass the existing XSS protection mechanisms.
The technical implementation of this vulnerability stems from inadequate input validation within TYPO3's URL sanitization logic. When users with authenticated access attempt to navigate through certain administrative interfaces, the system processes parameters such as returnUrl in show_rechis.php and redirect_url in index.php without properly decoding and validating base64 encoded data URIs. This allows attackers to embed malicious JavaScript code within these parameters that gets executed when the URLs are processed, effectively circumventing the intended security measures designed to prevent cross-site scripting attacks.
From an operational perspective, this vulnerability enables authenticated attackers to execute arbitrary JavaScript code in the context of a victim's browser session, potentially leading to session hijacking, data theft, or further compromise of the TYPO3 installation. The impact extends beyond simple XSS as it can facilitate more sophisticated attacks such as credential theft, privilege escalation, or redirection to malicious sites. Attackers can leverage this vulnerability to manipulate administrative interfaces and potentially gain unauthorized access to sensitive system configurations or user data. The vulnerability is particularly dangerous because it requires only authenticated access, meaning that users with legitimate administrative credentials could be exploited by attackers who compromise those accounts.
The security implications of this vulnerability align with CWE-79 which specifically addresses cross-site scripting flaws, and it maps to several ATT&CK techniques including T1059.007 for command and scripting interpreter and T1566 for credential harvesting. Organizations running affected TYPO3 versions should immediately implement mitigations including upgrading to patched versions, implementing additional input validation measures, and monitoring for suspicious administrative activities. The vulnerability demonstrates the critical importance of proper URL sanitization and the potential risks associated with insufficient validation of encoded data within web applications. Security teams should also consider implementing web application firewalls and additional monitoring for base64 encoded content within URL parameters to detect potential exploitation attempts.