CVE-2007-4137 in Trolltech
Summary
by MITRE
Off-by-one error in the QUtf8Decoder::toUnicode function in Trolltech Qt 3 allows context-dependent attackers to cause a denial of service (crash) via a crafted Unicode string that triggers a heap-based buffer overflow. NOTE: Qt 4 has the same error in the QUtf8Codec::convertToUnicode function, but it is not exploitable.
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Analysis
by VulDB Data Team • 07/25/2019
The vulnerability identified as CVE-2007-4137 represents a critical off-by-one error within the Unicode decoding functionality of Trolltech Qt 3 framework, specifically within the QUtf8Decoder::toUnicode function. This flaw constitutes a classic buffer overflow condition that occurs when processing Unicode strings, creating a scenario where the application fails to properly validate input boundaries during character conversion operations. The issue manifests as a heap-based buffer overflow, where the application attempts to write data beyond the allocated memory boundaries, leading to unpredictable behavior and potential system instability.
The technical implementation of this vulnerability stems from improper boundary checking within the Unicode decoding algorithm, where the QUtf8Decoder function fails to account for the exact number of bytes required for valid UTF-8 character sequences. This off-by-one error creates a scenario where maliciously crafted Unicode strings can trigger memory corruption by writing one byte beyond the intended buffer limits. The vulnerability is context-dependent, meaning that the attack requires specific conditions to be met, including the presence of the Qt 3 framework and the execution of code that processes Unicode input through the affected decoding function. According to CWE-129, this represents an implementation flaw where insufficient input validation leads to buffer overflow conditions that can be exploited for denial of service attacks.
The operational impact of CVE-2007-4137 is significant within applications that rely on Qt 3 for Unicode text processing, as it can be leveraged to cause system crashes and denial of service conditions. Attackers can craft specific Unicode strings that, when processed by vulnerable applications, will trigger the buffer overflow and subsequent application crash. This makes the vulnerability particularly dangerous in web applications, desktop applications, and any software that handles user-supplied Unicode text input. The vulnerability affects applications that use the Qt 3 framework for text processing, including but not limited to web browsers, text editors, and communication software that utilize Qt 3 libraries for handling international text encoding.
While Qt 4 contains the same fundamental error in the QUtf8Codec::convertToUnicode function, the vulnerability is noted as non-exploitable in that version, indicating that the implementation differences between Qt 3 and Qt 4 provide sufficient protections against exploitation. This distinction highlights the importance of proper input validation and boundary checking in cryptographic and text processing libraries, as similar flaws in different versions may have varying exploitability profiles. The vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks through application-level exploitation, and demonstrates how low-level library vulnerabilities can cascade into broader system availability issues.
The recommended mitigation strategies for CVE-2007-4137 include immediate migration to Qt 4 or newer versions that have addressed this vulnerability, implementation of proper input validation routines that check UTF-8 sequence boundaries before processing, and deployment of application-level defenses such as input sanitization and boundary checking. Organizations should also consider implementing intrusion detection systems that can identify patterns of Unicode string processing that may indicate exploitation attempts, and conduct regular security assessments of applications that rely on Qt 3 frameworks to identify potential exposure to similar vulnerabilities. The fix requires careful attention to proper memory management and boundary checking in Unicode processing functions, as specified in industry best practices for secure coding standards.