CVE-2000-0621 in Outlook
Summary
by MITRE
Microsoft Outlook 98 and 2000, and Outlook Express 4.0x and 5.0x, allow remote attackers to read files on the client s system via a malformed HTML message that stores files outside of the cache, aka the "Cache Bypass" vulnerability.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 05/08/2019
The CVE-2000-0621 vulnerability represents a critical security flaw in Microsoft Outlook 98 and 2000, along with Outlook Express 4.0x and 5.0x versions, which enables remote attackers to access arbitrary files on vulnerable client systems through carefully crafted malicious HTML messages. This vulnerability operates by exploiting improper handling of HTML content within the email client's caching mechanism, allowing attackers to bypass normal file access restrictions and retrieve sensitive information from the local system. The flaw specifically targets the way these email applications process HTML messages that contain malformed file references, enabling attackers to manipulate the cache storage locations and access files that should normally be restricted. This issue falls under the broader category of insecure file handling and improper input validation, which aligns with CWE-22 (Improper Limitation of a Pathname to a Restricted Directory) and CWE-73 (External Control of File Name or Path) classifications. The vulnerability demonstrates how email clients can be exploited to perform unauthorized file system operations, creating a pathway for data exfiltration and potential system compromise. From an operational perspective, this vulnerability poses significant risks to organizations relying on these older email clients, as it allows attackers to bypass traditional network-based security controls and directly access local files, potentially including sensitive documents, configuration files, or system information. The attack vector leverages the trust relationship between the email client and the user, as users typically expect to receive legitimate email content without considering the potential for file system exploitation. This vulnerability is particularly dangerous because it requires no special privileges on the target system beyond having the vulnerable email client installed, making it an attractive target for attackers seeking to gain unauthorized access to file systems. The security implications extend beyond simple file reading, as attackers could potentially access configuration files containing passwords, system settings, or other sensitive data that could be used for further exploitation. The attack mechanism specifically targets the HTML rendering engine's cache handling capabilities, where malformed HTML messages containing file references can cause the application to store and access files outside of normal cache boundaries. This behavior creates an indirect code execution pathway and allows for arbitrary file system traversal, making it a significant concern for enterprise environments where these legacy applications may still be in use. The vulnerability's impact is further amplified by the widespread adoption of these email clients in corporate environments, where users may not be aware of the security risks associated with processing untrusted HTML content. Organizations should consider implementing email filtering solutions, disabling HTML rendering for untrusted sources, and ensuring all systems are updated to newer versions of Microsoft Office that address this vulnerability. The remediation efforts should also include user education about the dangers of opening suspicious email attachments or clicking on unknown links, as well as implementing network-based security controls to prevent the delivery of malicious HTML content. This vulnerability highlights the importance of proper input validation and secure file handling practices, particularly in applications that process untrusted content from external sources, and serves as a reminder of the ongoing need for security updates and patch management across legacy systems. The ATT&CK framework categorizes this vulnerability under T1190 (Exploit Public-Facing Application) and T1059 (Command and Scripting Interpreter) due to the exploitation of application vulnerabilities and potential subsequent command execution capabilities.