CVE-1999-0488 in Internet Explorer
Summary
by MITRE
Internet Explorer 4.0 and 5.0 allows a remote attacker to execute security scripts in a different security context using malicious URLs, a variant of the "cross frame" vulnerability.
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Analysis
by VulDB Data Team • 04/19/2026
This vulnerability represents a critical cross-frame scripting security flaw that affected Microsoft Internet Explorer versions 4.0 and 5.0 released in the late 1990s. The vulnerability stems from how these browsers handled frame navigation and security context boundaries, allowing malicious actors to exploit the trust relationship between frames to execute unauthorized scripts. The flaw specifically enabled attackers to inject scripts into different security contexts through carefully crafted malicious URLs, effectively bypassing the browser's security model that was designed to isolate content from different origins. This cross-frame scripting variant exploited the fundamental security assumption that frames from different domains should be isolated from each other, creating a pathway for privilege escalation and unauthorized code execution.
The technical implementation of this vulnerability relied on the browser's frame handling mechanisms and how it managed security contexts when navigating between different frames within the same document. When a user visited a malicious URL containing crafted frame references, the browser would incorrectly process the navigation sequence, allowing a script embedded in one frame to access or manipulate the security context of another frame. This behavior violated the same-origin policy that browsers implement to prevent unauthorized cross-domain access, creating a scenario where scripts from less trusted sources could execute within the security context of more trusted domains. The vulnerability was particularly dangerous because it could be exploited through social engineering attacks where users would be tricked into visiting malicious websites that contained the crafted URLs.
The operational impact of this vulnerability was severe as it allowed remote attackers to perform various malicious activities including credential theft, session hijacking, and data exfiltration. Attackers could craft malicious web pages that would automatically execute scripts in the context of a user's active browsing session, potentially accessing sensitive information or performing unauthorized actions on behalf of the user. The vulnerability was especially concerning because it affected widely deployed versions of Internet Explorer, meaning millions of users were potentially exposed to this attack vector. Security researchers noted that this flaw could be combined with other vulnerabilities to create more sophisticated attacks, making it a significant concern for enterprise environments where users might access both internal and external web resources.
This vulnerability aligns with CWE-79 which describes cross-site scripting flaws, and demonstrates the importance of proper input validation and context-aware security controls in web browsers. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and credential access through browser-based attacks. The flaw highlighted the critical importance of maintaining strict security boundaries between different content contexts within web browsers and demonstrated how seemingly minor implementation issues in browser security models could have major consequences. Organizations had to implement immediate patches and workarounds to protect their users, while security researchers emphasized the need for more rigorous testing of browser security models. The vulnerability also underscored the importance of keeping browser software updated and implementing additional security measures such as content filtering and security policy enforcement to mitigate the risk of exploitation.
The remediation approach for this vulnerability required immediate patching of affected Internet Explorer versions, along with user education about the risks of visiting untrusted websites. Browser vendors had to enhance their frame handling mechanisms to properly enforce security boundaries, and organizations needed to implement additional protective measures such as web application firewalls and security policy controls. The incident served as a catalyst for improved browser security standards and highlighted the ongoing challenge of securing complex web browsing environments against sophisticated attack vectors that exploit subtle implementation flaws in security models.