CVE-2007-1749 in Windows
Summary
by MITRE
Integer underflow in the CDownloadSink class code in the Vector Markup Language (VML) component (VGX.DLL), as used in Internet Explorer 5.01, 6, and 7 allows remote attackers to execute arbitrary code via compressed content with an invalid buffer size, which triggers a heap-based buffer overflow.
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Analysis
by VulDB Data Team • 01/13/2025
The vulnerability described in CVE-2007-1749 represents a critical security flaw in the Vector Markup Language (VML) component of Internet Explorer versions 5.01, 6, and 7. This issue resides within the CDownloadSink class code in the VGX.DLL library, which handles the processing of VML content within web browsers. The vulnerability stems from improper handling of compressed content where an invalid buffer size is encountered during the decompression process, creating a dangerous condition that can be exploited by remote attackers.
The technical implementation of this vulnerability involves an integer underflow condition that occurs when processing compressed VML content. When Internet Explorer encounters compressed data that contains an invalid buffer size parameter, the integer underflow causes the application to allocate insufficient memory for the decompressed content. This insufficient allocation leads to a heap-based buffer overflow scenario where attacker-controlled data can overwrite adjacent memory locations. The flaw specifically manifests in the VML component's decompression routine where the integer arithmetic fails to properly validate the buffer size parameters, resulting in a situation where the allocated memory space becomes smaller than the actual data being written.
The operational impact of this vulnerability is severe as it provides remote attackers with the capability to execute arbitrary code on vulnerable systems. The heap-based buffer overflow allows attackers to manipulate memory layout and potentially redirect execution flow to malicious code injected into the heap. This type of vulnerability falls under CWE-128, which specifically addresses integer underflow conditions that can lead to buffer overflows, and aligns with ATT&CK technique T1059.007 for command and scripting interpreter. The vulnerability affects multiple versions of Internet Explorer, making it particularly dangerous as it could impact a wide range of systems in enterprise environments where older browser versions might still be in use.
The exploitation of this vulnerability requires an attacker to host malicious VML content that contains compressed data with malformed buffer size parameters. When a user's browser attempts to process this content, the integer underflow triggers the buffer overflow condition. The memory corruption can be leveraged to execute shellcode or other malicious payloads, potentially leading to complete system compromise. The vulnerability is particularly concerning because it can be triggered through normal web browsing activities without requiring user interaction beyond visiting a malicious website. Organizations should consider implementing security mitigations such as disabling VML support, using modern browser versions with proper memory protection mechanisms, and deploying intrusion detection systems to monitor for exploitation attempts. The vulnerability also highlights the importance of proper input validation and integer overflow protection in legacy code components that continue to be used in modern applications.