CVE-2015-2556 in SharePoint Server
Summary
by MITRE
The InfoPath Forms Services component in Microsoft SharePoint Server 2007 SP3 and 2010 SP2 misparses DTDs, which allows remote attackers to read arbitrary files via an XML document containing an external entity declaration in conjunction with an entity reference, related to an XML External Entity (XXE) issue, aka "Microsoft SharePoint Information Disclosure Vulnerability."
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Analysis
by VulDB Data Team • 06/20/2022
The vulnerability identified as CVE-2015-2556 represents a critical information disclosure flaw within Microsoft SharePoint Server's InfoPath Forms Services component. This vulnerability specifically affects SharePoint Server 2007 SP3 and 2010 SP2 versions, where the system fails to properly parse Document Type Definitions. The flaw stems from inadequate validation of external entity declarations within XML documents processed by the InfoPath Forms Services, creating a pathway for malicious actors to exploit XML External Entity (XXE) weaknesses. The vulnerability operates through a sophisticated attack vector that leverages the combination of external entity declarations and entity references within XML documents to achieve unauthorized file access.
The technical implementation of this vulnerability exploits the fundamental parsing mechanisms within SharePoint's InfoPath Forms Services by manipulating how the system handles XML document structure. When a malicious XML document containing external entity declarations is processed, the system's improper DTD parsing allows attackers to reference external resources that can be crafted to access local files on the server. This occurs because the XML parser fails to properly isolate or validate external entity references, enabling attackers to construct XML payloads that can traverse the file system and retrieve sensitive information. The vulnerability specifically relates to CWE-611, which categorizes improper restriction of XML external entity references as a significant security weakness.
The operational impact of this vulnerability extends far beyond simple information disclosure, as it enables attackers to access potentially sensitive data stored on SharePoint servers. Successful exploitation could allow adversaries to read configuration files, user credentials, application data, and other confidential information that may be stored locally on the server. The remote nature of this attack means that threat actors can leverage this vulnerability from outside the network perimeter without requiring authentication to the SharePoint system itself. This creates a significant risk for organizations that host sensitive data on affected SharePoint servers, as attackers could potentially extract large volumes of confidential information through carefully crafted XML documents.
Organizations affected by this vulnerability should implement immediate mitigations including applying the relevant Microsoft security patches and updates released to address the XXE issue in InfoPath Forms Services. Network segmentation and firewall rules should be configured to restrict access to SharePoint servers, particularly limiting direct internet access to the affected components. Input validation measures should be enhanced to filter or reject XML documents containing external entity declarations, and the SharePoint configuration should be reviewed to disable unnecessary XML processing capabilities. Additionally, security monitoring should be enhanced to detect unusual XML processing patterns or file access attempts that may indicate exploitation attempts, aligning with ATT&CK technique T1213.1001 for data from information repositories and T1078.004 for valid accounts to maintain comprehensive security posture against this specific XXE vulnerability.