CVE-1999-0870 in Internet Explorer
Summary
by MITRE
Internet Explorer 4.01 allows remote attackers to read arbitrary files by pasting a file name into the file upload control, aka untrusted scripted paste.
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Analysis
by VulDB Data Team • 04/17/2026
This vulnerability exists in Microsoft Internet Explorer version 4.01 and represents a significant security flaw in the browser's handling of file upload controls. The issue stems from insufficient validation of user input within the file upload interface, allowing remote attackers to manipulate the file path through script injection techniques. When users interact with file upload controls in the browser, the application fails to properly sanitize or validate the file path data, creating an opportunity for malicious actors to access unauthorized files on the target system. The vulnerability specifically exploits the browser's scripting capabilities to construct malicious file paths that bypass normal access controls.
The technical exploitation of this vulnerability involves crafting malicious scripts that can be pasted into file upload controls, effectively bypassing the intended file selection mechanisms. Attackers can leverage this flaw to read arbitrary files from the local filesystem, potentially accessing sensitive data such as configuration files, user credentials, or system information. The vulnerability operates under the broader category of input validation flaws, specifically related to improper handling of file system paths within web browser environments. This type of vulnerability falls under CWE-20, which encompasses improper input validation, and represents a classic example of how browser-based scripting can be abused to perform unauthorized file operations.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can enable more sophisticated attacks including privilege escalation and system compromise. An attacker who successfully exploits this vulnerability can potentially gain access to sensitive files that should normally be protected from unauthorized access, leading to data breaches and system infiltration. The attack vector is particularly concerning because it can be executed remotely without requiring local system access, making it a significant threat to web application security. This vulnerability directly impacts the principle of least privilege by allowing unauthorized file access through browser interfaces that should normally be restricted to legitimate file operations.
Mitigation strategies for this vulnerability should focus on implementing proper input validation and sanitization within browser-based file handling mechanisms. Organizations should ensure that all file upload controls properly validate file paths and reject potentially malicious input patterns. The recommended approach includes implementing strict file path validation, using secure coding practices for web applications, and applying appropriate access controls to prevent unauthorized file system access. Security professionals should also consider implementing network-level protections such as web application firewalls and intrusion detection systems to monitor for suspicious file access patterns. Additionally, regular security updates and patches should be applied to ensure that browsers and web applications are protected against known vulnerabilities. This vulnerability highlights the importance of comprehensive security testing including input validation testing and secure coding practices in web application development, aligning with ATT&CK technique T1059.007 for script-based attacks and T1566 for social engineering through malicious file downloads.