CVE-2002-0500 in Internet Explorer
Summary
by MITRE
Internet Explorer 5.0 through 6.0 allows remote attackers to determine the existence of files on the client via an IMG tag with a dynsrc property that references the target file, which sets certain elements of the image object such as file size.
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Analysis
by VulDB Data Team • 05/07/2019
This vulnerability exists in internet explorer versions 5.0 through 6.0 and represents a classic information disclosure flaw that exploits the dynamic image loading mechanism. The vulnerability specifically leverages the dynsrc property within html img tags to indirectly reveal file existence information on compromised client systems. When a malicious attacker crafts an html page containing an img tag with a dynsrc attribute pointing to a target file, the browser processes this request and populates certain image object properties including file size information. This behavior occurs because the browser attempts to load and process the referenced resource, even when it's not a traditional image file, thereby exposing metadata about the target file through the dynamic loading process.
The technical implementation of this vulnerability stems from how internet explorer handles dynamic image loading through the dynsrc attribute, which was designed to support animated gif files and other dynamic content. However, the implementation failed to properly sanitize or validate the target resource references, allowing attackers to probe for file existence by observing the response characteristics. When the browser attempts to load the target file through the dynsrc mechanism, it sets specific properties of the image object that contain file size and other metadata, creating a side-channel information leak. This type of vulnerability falls under the category of information disclosure issues and can be classified as a variant of cwe-200 information exposure, where unintended information is revealed through application behavior rather than direct exploitation.
The operational impact of this vulnerability extends beyond simple file enumeration, as it enables attackers to perform reconnaissance activities against client systems without direct access to the target environment. An attacker could potentially map out file structures on a victim's system by repeatedly attempting to load various file paths and observing the response characteristics. This information disclosure capability allows for more sophisticated attacks, including targeted exploitation of specific file types or the identification of sensitive files that might be present on the system. The vulnerability particularly affects environments where internet explorer 5.0 through 6.0 is still in use, representing a significant security risk in legacy systems. From an attack perspective, this vulnerability aligns with techniques described in the attack pattern taxonomy under the category of reconnaissance and information gathering, where attackers seek to understand the target environment before launching more direct attacks.
The primary mitigation strategy involves avoiding the use of internet explorer versions 5.0 through 6.0, as these versions are inherently vulnerable to this class of attack. Organizations should implement web application firewalls that can detect and block suspicious img tag patterns with dynsrc attributes, particularly when they reference potentially sensitive file paths. Additionally, administrators should consider implementing proper input validation and sanitization for dynamic content loading mechanisms, ensuring that any external resource references are properly validated against known safe patterns. The vulnerability demonstrates the importance of proper resource handling and validation in web browsers, as it highlights how seemingly benign features like dynamic image loading can be exploited for information gathering purposes. Security practitioners should also consider implementing monitoring solutions that can detect anomalous image loading patterns and alert on potential information disclosure attempts, as this vulnerability represents a significant risk in environments where legacy browser support is required.