CVE-1999-0877 in Internet Explorer
Summary
by MITRE
Internet Explorer 5 allows remote attackers to read files via an ExecCommand method called on an IFRAME.
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Analysis
by VulDB Data Team • 02/28/2025
The vulnerability identified as CVE-1999-0877 represents a significant security flaw in Internet Explorer 5 that exploited the browser's handling of the ExecCommand method when invoked on IFRAME elements. This vulnerability falls under the broader category of cross-site scripting and privilege escalation attacks that were prevalent during the late 1990s web browser security landscape. The issue specifically targeted the way Internet Explorer processed certain commands executed within embedded frames, creating an avenue for malicious actors to access files on the victim's system that they should not be able to read. This flaw exploited the browser's security model by leveraging the trust relationship between the browser and its embedded content, particularly when executing commands that should have been restricted to the browser's own domain.
The technical implementation of this vulnerability relied on the ExecCommand method's improper validation of parameters when called on IFRAME elements. When a malicious web page executed the ExecCommand method with specific parameters on an IFRAME, it could potentially access or read files from the local filesystem that were otherwise protected by the browser's security restrictions. The vulnerability was particularly dangerous because it could be triggered through standard web browsing activities without requiring any special user interaction beyond visiting a compromised website. The flaw essentially bypassed the browser's normal security boundaries, allowing remote attackers to execute commands that should have been confined to the browser's own execution context rather than being available to arbitrary web content within embedded frames.
The operational impact of this vulnerability was substantial as it enabled attackers to perform unauthorized file access operations on victims' systems. This capability could be exploited to read sensitive information from local files, potentially including configuration files, user data, or even system files that should have remained protected. The attack vector was particularly insidious because it required no local privileges or special software installations on the victim's machine beyond standard web browsing. Attackers could craft malicious web pages that would automatically attempt to read files when loaded in Internet Explorer 5, making this a passive attack that could be deployed at scale. The vulnerability's exploitation could lead to information disclosure, system reconnaissance, and potentially further compromise of the victim's system through the acquisition of sensitive data that could be used in subsequent attacks.
This vulnerability aligns with CWE-20, which describes improper input validation, and represents a classic example of how browser security models can be circumvented through improper handling of cross-domain operations. The attack pattern corresponds to techniques described in the ATT&CK framework under T1059.001 for command and scripting interpreters, specifically targeting the browser's scripting capabilities to execute unauthorized operations. Organizations and security professionals should have implemented immediate mitigations including browser updates, network-level filtering to block suspicious content, and user education about visiting untrusted websites. The vulnerability also highlighted the need for better sandboxing mechanisms in web browsers and proper isolation between different security contexts within the browser environment. Modern browsers have since addressed similar issues through improved security boundaries, stricter input validation, and more robust implementation of the same-origin policy that prevents such unauthorized cross-domain file access operations.