CVE-2015-2543 in Exchange Server
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in Outlook Web Access (OWA) in Microsoft Exchange Server 2013 Cumulative Update 8 and 9 allows remote attackers to inject arbitrary web script or HTML via a crafted e-mail message, aka "Exchange Spoofing Vulnerability."
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Analysis
by VulDB Data Team • 06/14/2022
The CVE-2015-2543 vulnerability represents a critical cross-site scripting flaw in Microsoft Exchange Server 2013's Outlook Web Access component, specifically affecting Cumulative Updates 8 and 9. This vulnerability operates as a spoofing attack vector that enables remote threat actors to execute malicious scripts within the context of a victim's browser session. The flaw manifests when users receive crafted email messages that contain malicious payloads designed to exploit the XSS vulnerability in the web-based email interface. The vulnerability stems from insufficient input validation and output encoding within the OWA rendering pipeline, creating an exploitable condition where untrusted data flows directly into the browser without proper sanitization. This issue directly maps to CWE-79, which describes Cross-site Scripting vulnerabilities, and falls under the broader category of web application security flaws that compromise user session integrity and data confidentiality. The attack surface is particularly concerning as it leverages the trusted email delivery mechanism to deliver malicious content, bypassing traditional email filtering mechanisms that might not detect such sophisticated payload delivery methods.
The technical exploitation of this vulnerability occurs through the manipulation of email message content that gets rendered in the Outlook Web Access interface. When a victim opens a maliciously crafted email, the crafted HTML or JavaScript code embedded within the message is executed in the context of the victim's authenticated session within OWA. This creates a persistent threat where attackers can perform actions on behalf of the victim, potentially accessing sensitive email content, modifying user settings, or even escalating privileges within the Exchange environment. The vulnerability specifically targets the way OWA processes and displays email content, particularly when handling certain HTML elements or script tags that are not properly escaped or filtered during the rendering process. The attack requires minimal user interaction beyond simply opening the malicious email message, making it particularly dangerous in enterprise environments where users frequently interact with email communications. This vulnerability aligns with ATT&CK technique T1566, which covers Spearphishing Attachments, and demonstrates how email-based attacks can be amplified through web application flaws to achieve more significant security breaches.
The operational impact of CVE-2015-2543 extends beyond simple script execution, as it provides attackers with persistent access to user email accounts and potentially broader network resources within the Exchange infrastructure. Successful exploitation can lead to unauthorized access to sensitive business communications, credential theft through session hijacking, and the potential for lateral movement within the network. The vulnerability affects organizations using Exchange Server 2013 with the specified cumulative updates, creating a widespread risk across enterprises that rely on web-based email access for business operations. Organizations may experience data breaches, regulatory compliance violations, and reputational damage when this vulnerability is exploited successfully. The threat actor can leverage the authenticated context to perform actions such as reading all emails, sending messages on behalf of the user, accessing calendar information, and potentially accessing other resources within the Exchange environment that are protected by the same authentication mechanism. This vulnerability also creates opportunities for attackers to establish persistent backdoors or use the compromised session for further reconnaissance activities. The impact is particularly severe in environments where Exchange servers are directly exposed to the internet or where users frequently access email through web interfaces, as these scenarios provide the most straightforward attack paths for exploitation. Organizations should consider implementing comprehensive security monitoring to detect unusual email access patterns or suspicious script execution within their Exchange environments, as these indicators may suggest exploitation attempts. The vulnerability underscores the importance of maintaining up-to-date security patches and implementing robust email security measures that go beyond traditional spam filtering to include advanced threat detection and content inspection capabilities.