CVE-1999-0870 is a vulnerability found in Microsoft Internet Explorer version 4.01, disclosed in 1998. The issue arises from the browser's handling of the file upload control, specifically allowing remote attackers to read arbitrary files on the victim's system by pasting a file name into the file upload input field. This vulnerability is commonly referred to as "untrusted scripted paste." Essentially, the attacker can exploit the browser's insufficient validation and security controls around clipboard operations and file input fields to trick the browser into revealing local file contents. The vulnerability does not require user authentication but does require user interaction in the form of pasting a file path into the upload control. The attack vector is network-based, where the attacker lures the victim to a malicious webpage. The CVSS v2 score is 2.6, indicating a low severity primarily due to the high attack complexity and the need for user interaction. The impact is limited to confidentiality as the attacker can read files but cannot modify or delete them, nor cause denial of service. Microsoft issued a patch (MS98-015) to address this vulnerability, which involves tightening the security around file upload controls and clipboard operations in Internet Explorer 4.01. Given the age of the vulnerability and the obsolescence of Internet Explorer 4.01, this issue is largely historical but remains relevant for legacy systems still running this outdated browser version.

For European organizations, the direct impact of this vulnerability today is minimal due to the obsolescence of Internet Explorer 4.01. However, if legacy systems or industrial control environments still use this outdated browser, there is a risk of unauthorized disclosure of sensitive local files. This could lead to leakage of confidential information, internal configuration files, or credentials stored locally. The vulnerability could be exploited by attackers through crafted web pages, potentially leading to targeted espionage or data leakage. The low severity and requirement for user interaction reduce the likelihood of widespread exploitation. Nonetheless, organizations with legacy infrastructure or those in sectors with long technology refresh cycles (e.g., manufacturing, utilities) should be aware of this risk. The vulnerability does not affect modern browsers or supported versions of Internet Explorer, so the impact on most European enterprises is negligible.

The primary mitigation is to ensure that all systems are updated to supported and patched versions of browsers. Specifically, any system running Internet Explorer 4.01 should be upgraded or replaced immediately. Applying the Microsoft security bulletin MS98-015 patch is essential if the legacy browser must remain in use. Additionally, organizations should restrict or disable the use of outdated browsers through group policies or endpoint management tools. Network-level controls such as web filtering and blocking access to known malicious sites can reduce exposure. User education to avoid pasting file paths into untrusted web forms is also beneficial. For environments where legacy browsers cannot be removed, isolating these systems from the internet and limiting their access to trusted internal resources can reduce risk. Finally, monitoring for unusual file access or exfiltration attempts on endpoints can help detect exploitation attempts.