CVE-2007-0242 in Qt
Summary
by MITRE
The UTF-8 decoder in codecs/qutfcodec.cpp in Qt 3.3.8 and 4.2.3 does not reject long UTF-8 sequences as required by the standard, which allows remote attackers to conduct cross-site scripting (XSS) and directory traversal attacks via long sequences that decode to dangerous metacharacters.
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Analysis
by VulDB Data Team • 07/17/2019
The vulnerability described in CVE-2007-0242 represents a critical flaw in the Qt framework's UTF-8 decoding implementation that has significant implications for web application security. This issue affects Qt versions 3.3.8 and 4.2.3, where the codecs/qutfcodec.cpp file fails to properly validate UTF-8 sequences according to established standards. The flaw specifically manifests when the decoder accepts overly long UTF-8 sequences that should be rejected as invalid according to the Unicode standard. This improper handling creates a security boundary that attackers can exploit to bypass input validation mechanisms and inject malicious content into applications that rely on Qt for their user interface components.
The technical nature of this vulnerability stems from the failure to enforce proper UTF-8 sequence length validation during the decoding process. In standard UTF-8 encoding, sequences must adhere to specific length constraints that prevent the creation of invalid byte combinations. When Qt's decoder accepts sequences that exceed these legitimate bounds, it can produce decoded output that contains dangerous characters or sequences that are interpreted as metacharacters by web browsers or application frameworks. This behavior creates a path for attackers to craft malicious input that appears valid to the application's input sanitization but actually decodes to harmful content when processed by the Qt framework.
The operational impact of this vulnerability extends beyond simple XSS attacks to include directory traversal exploits and other injection-based attacks. When attackers can manipulate UTF-8 sequences to produce decoded content that contains path traversal characters or script execution directives, they can effectively bypass security controls that assume input validation has been properly enforced. The vulnerability allows for the exploitation of applications that depend on Qt for their interface components, particularly web applications that process user input through Qt-based frameworks. This creates a vector where attackers can inject malicious payloads that are then interpreted by the browser or application framework, potentially leading to complete system compromise or unauthorized data access.
This vulnerability aligns with CWE-180, which addresses the issue of incorrect behavior in input validation, and can be mapped to ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation' through the exploitation of input validation flaws. The weakness creates a persistent security gap that can be leveraged across multiple attack vectors including cross-site scripting, directory traversal, and potentially other injection attacks that rely on bypassing input sanitization. Organizations using affected Qt versions must understand that this vulnerability creates a fundamental flaw in the application's ability to properly validate and sanitize user input, potentially allowing attackers to circumvent security controls that depend on proper UTF-8 handling.
The recommended mitigation strategy involves immediate upgrading to patched versions of the Qt framework where the UTF-8 decoder properly enforces standard compliance. Additionally, applications that cannot immediately upgrade should implement additional input validation layers that explicitly check for and reject malformed UTF-8 sequences before they reach the Qt framework. Security teams should also consider implementing web application firewalls or other protective measures that can detect and block suspicious UTF-8 sequences that may be attempting to exploit this vulnerability. The long-term solution requires comprehensive testing of all input handling components to ensure compliance with Unicode standards and proper validation of character encoding throughout the application stack.