CVE-2004-0502 in Outlook
Summary
by MITRE
Outlook 2003, when replying to an e-mail message, stores certain files in a predictable location for the "src" of an img tag of the original message, which allows remote attackers to bypass zone restrictions and exploit other issues that rely on predictable locations, as demonstrated using a shell: URI.
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Analysis
by VulDB Data Team • 09/17/2025
This vulnerability exists in Microsoft Outlook 2003 where the application stores certain files in predictable locations when replying to email messages. The flaw specifically affects how Outlook handles the "src" attribute of img tags in HTML email messages. When a user replies to an email containing an image tag with a source URI, Outlook creates temporary files in well-known, predictable directory paths on the local system. This behavior creates a significant security risk because it allows remote attackers to exploit the predictable file placement to bypass security zone restrictions that normally protect users from executing malicious code.
The technical implementation of this vulnerability stems from Outlook's handling of HTML email content during reply operations. When processing HTML messages containing img tags, Outlook does not properly sanitize or randomize the temporary file locations where it stores referenced resources. This predictable storage pattern means that an attacker who can craft an HTML email message with a malicious img tag can potentially place files in locations that are accessible to other security contexts, particularly those that rely on zone-based security models. The vulnerability becomes particularly dangerous when combined with other attack vectors that depend on predictable file locations.
The operational impact of this vulnerability extends beyond simple file placement issues and can enable more sophisticated attacks. The vulnerability allows attackers to bypass zone restrictions that are typically enforced by Microsoft's security model, where different security zones (internet, local intranet, trusted sites, etc.) have different permission levels for executing code or accessing system resources. When combined with shell: URI schemes or other malicious constructs, this vulnerability can potentially enable attackers to execute arbitrary code with the privileges of the user running Outlook. The predictable file locations essentially provide a foothold for privilege escalation attacks or code injection attempts that would otherwise be prevented by normal security boundaries.
The security implications of this vulnerability align with CWE-22 which describes improper limitation of a pathname to a restricted directory, also known as path traversal. This weakness allows attackers to access files and directories that are stored outside the intended directory, by manipulating variables that reference files with "dot-dot-slash" (../) sequences and directory separators. The vulnerability also relates to ATT&CK technique T1059 which covers command and scripting interpreters, as the ability to place files in predictable locations can enable attackers to execute malicious scripts or commands through compromised email clients. Additionally, the vulnerability demonstrates characteristics of T1133 which involves external remote services, as it allows attackers to manipulate local file systems through remote email messages.
Mitigation strategies for this vulnerability should focus on both immediate protective measures and long-term architectural improvements. Users should avoid replying to untrusted email messages that contain HTML content, particularly those with embedded img tags or other potentially malicious HTML elements. Microsoft recommended applying security updates and patches as soon as they became available, though this specific vulnerability was addressed through broader security improvements in later versions of Outlook. Organizations should implement email filtering solutions that can detect and block potentially malicious HTML content, particularly images with suspicious source URIs. The vulnerability also underscores the importance of maintaining up-to-date security practices, as the predictable file placement behavior was part of a broader class of issues that affected email clients and web browsers in the early 2000s, highlighting the need for robust input validation and secure temporary file handling in all applications that process user-supplied content.