CVE-2001-0726 in Exchange
Summary
by MITRE
Outlook Web Access (OWA) in Microsoft Exchange 5.5 Server, when used with Internet Explorer, does not properly detect certain inline script, which can allow remote attackers to perform arbitrary actions on a user s Exchange mailbox via an HTML e-mail message.
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Analysis
by VulDB Data Team • 10/04/2025
Microsoft Exchange 5.5 Server with Outlook Web Access functionality presents a critical security vulnerability that stems from insufficient validation of inline script content within HTML email messages. This vulnerability specifically affects the interaction between OWA and Internet Explorer browsers, creating a pathway for remote attackers to execute unauthorized actions on user mailboxes without requiring authentication. The flaw resides in the improper detection mechanism that fails to adequately identify and neutralize potentially malicious script code embedded within HTML formatted emails. When users access their mailboxes through OWA, the system processes incoming HTML messages without sufficient sanitization of script elements, allowing attackers to craft specially formatted emails that contain embedded malicious code. This vulnerability operates at the application layer and represents a classic cross-site scripting attack vector that leverages the trust relationship between the user's browser and the Exchange server. The technical implementation flaw manifests when the web interface processes HTML content without proper input validation, failing to distinguish between legitimate and malicious script execution contexts. This weakness directly corresponds to CWE-79 which defines improper neutralization of input during web page generation, specifically targeting script injection vulnerabilities. The attack surface extends beyond simple message viewing to encompass full mailbox manipulation capabilities, including message deletion, forwarding, and potentially unauthorized access to sensitive data.
The operational impact of this vulnerability is substantial as it enables attackers to perform arbitrary actions on compromised user mailboxes without requiring any form of authentication or privileged access. Remote threat actors can exploit this weakness by simply sending malicious HTML emails to targeted users, making the attack vector extremely accessible and scalable. Once a user opens the malicious email through OWA, the embedded script executes within the browser context, potentially allowing attackers to access, modify, or delete mailbox contents. The vulnerability creates a persistent threat where attackers can establish footholds within organizations by compromising individual user accounts through this method. The attack follows the typical patterns described in ATT&CK technique T1190 for exploitation of web applications, specifically targeting the server-side web application interface rather than client-side vulnerabilities. This weakness essentially transforms the legitimate web-based email access functionality into an attack surface that can be leveraged for unauthorized mailbox manipulation, making it particularly dangerous in enterprise environments where Exchange servers handle sensitive corporate communications. The vulnerability also aligns with ATT&CK technique T1078 for valid accounts, as compromised user sessions can be used to maintain persistent access to mailbox resources.
Mitigation strategies for this vulnerability should focus on implementing comprehensive input validation and sanitization mechanisms within the Exchange server's web interface processing pipeline. Organizations must ensure that all HTML content received through OWA is properly sanitized before display, removing or neutralizing any potentially malicious script elements. The implementation should include strict content filtering rules that prevent execution of inline scripts within email messages, particularly those that could interact with the underlying Exchange server functionality. Security patches and updates from Microsoft should be deployed immediately to address the root cause of the vulnerability, as the company provided specific fixes for this issue in subsequent releases. Network-level protections such as email filtering systems should be enhanced to detect and quarantine suspicious HTML content before it reaches the Exchange server. Additionally, user education regarding the dangers of opening suspicious emails and the implementation of secure browsing practices within the OWA environment can help reduce the likelihood of exploitation. Organizations should also consider implementing additional monitoring and logging mechanisms to detect unusual mailbox activity that might indicate successful exploitation attempts. The remediation process should include thorough testing of the sanitization mechanisms to ensure they do not inadvertently break legitimate email functionality while effectively blocking malicious content. Regular security assessments of web-based email systems should be conducted to identify similar vulnerabilities in other components of the email infrastructure that may present comparable risks.