CVE-2000-0753 in Outlook
Summary
by MITRE
The Microsoft Outlook mail client identifies the physical path of the sender s machine within a winmail.dat attachment to Rich Text Format (RTF) files.
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Analysis
by VulDB Data Team • 05/16/2019
The vulnerability described in CVE-2000-0753 represents a significant information disclosure flaw within Microsoft Outlook's handling of rich text format attachments. This issue specifically affects the processing of winmail.dat files which are generated when Outlook users send messages with rich text formatting to recipients who may not have Outlook installed. The vulnerability stems from the way Outlook embeds sender system information within these attachments, creating a potential avenue for attackers to gather sensitive environmental data about the originating system.
The technical flaw manifests when Outlook processes RTF-formatted messages containing embedded winmail.dat attachments. During this processing, the client inadvertently includes the physical path of the sender's machine within the attachment structure. This path information is typically stored in the winmail.dat file's internal metadata, which is designed to preserve formatting and embedded objects when messages are sent between Outlook users. However, when these attachments are processed by non-Outlook clients or when the attachment is analyzed by security tools, the embedded path information becomes accessible to unauthorized parties.
The operational impact of this vulnerability extends beyond simple information disclosure, as the physical path information can reveal critical system details including drive letters, directory structures, and potentially even network share locations. Attackers could leverage this information to conduct further reconnaissance activities, mapping network topologies, identifying system configurations, or planning more sophisticated attacks. The vulnerability is particularly concerning because it operates silently in the background without requiring user interaction, making it difficult to detect and prevent through standard user awareness training.
From a cybersecurity perspective, this vulnerability aligns with CWE-200, which addresses information exposure, and demonstrates how seemingly benign email processing features can create security risks. The ATT&CK framework categorizes this as a reconnaissance technique under initial access and defense evasion phases, where adversaries gather system information to inform their attack planning. The vulnerability's exploitation does not require elevated privileges or complex attack chains, making it particularly dangerous as it can be leveraged by threat actors with minimal technical expertise.
Mitigation strategies for this vulnerability should focus on both immediate and long-term solutions. Organizations should implement email filtering rules that block winmail.dat attachments or strip them from incoming messages before they reach end users. Security administrators should also consider configuring Outlook to disable rich text formatting for external communications or implement content filtering solutions that can identify and neutralize potentially malicious path information within attachments. Additionally, regular security awareness training should emphasize the risks of opening email attachments from untrusted sources, particularly when these attachments contain rich text formatting elements that may trigger such information disclosure behaviors.
The vulnerability highlights the importance of understanding how email client applications handle rich text formatting and embedded objects, as these features often create unexpected security implications. Organizations should conduct regular security assessments of their email infrastructure to identify similar information disclosure vulnerabilities that may exist in other components of their communication systems. Furthermore, this case underscores the necessity of maintaining up-to-date email client software and security patches, as Microsoft would have addressed this issue in subsequent releases through improved attachment handling mechanisms.