CVE-2019-0556 in SharePoint Enterprise Server
Summary
by MITRE
A cross-site-scripting (XSS) vulnerability exists when Microsoft SharePoint Server does not properly sanitize a specially crafted web request to an affected SharePoint server, aka "Microsoft Office SharePoint XSS Vulnerability." This affects Microsoft SharePoint. This CVE ID is unique from CVE-2019-0557, CVE-2019-0558.
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Analysis
by VulDB Data Team • 02/28/2025
The vulnerability described in CVE-2019-0556 represents a critical cross-site scripting flaw within Microsoft SharePoint Server that enables attackers to execute malicious scripts in the context of authenticated users. This vulnerability specifically manifests when the SharePoint server fails to adequately sanitize web requests containing crafted malicious input, creating an avenue for persistent security breaches. The flaw affects Microsoft Office SharePoint Server environments and demonstrates the ongoing challenges organizations face with web application security in enterprise collaboration platforms.
This XSS vulnerability operates through the manipulation of input validation mechanisms within SharePoint's web request processing pipeline. When a malicious user crafts a specially designed web request containing script payloads, the server's insufficient sanitization processes allow these malicious inputs to be stored and subsequently executed in the browsers of other users who access the affected content. The vulnerability's classification as a persistent XSS issue means that malicious scripts can be stored on the server and executed against multiple users over time, rather than requiring immediate interaction with the malicious page. This characteristic significantly amplifies the potential impact and persistence of attacks.
The operational impact of this vulnerability extends beyond simple script execution to encompass potential data theft, session hijacking, and privilege escalation within SharePoint environments. Attackers can leverage this flaw to steal user credentials, access sensitive documents, manipulate content, and potentially establish persistent backdoors within the SharePoint infrastructure. The vulnerability affects the core authentication and authorization mechanisms of SharePoint, potentially allowing unauthorized access to confidential information and administrative functions. Organizations utilizing SharePoint Server for document management, collaboration, and business-critical applications face significant risk exposure when this vulnerability remains unpatched.
Mitigation strategies for CVE-2019-0556 should prioritize immediate implementation of Microsoft security updates and patches to address the specific sanitization deficiencies in SharePoint Server. Organizations should also implement robust input validation controls, including comprehensive content security policy (CSP) headers, regular security assessments of SharePoint configurations, and enhanced monitoring of user activities for suspicious script injections. Network segmentation and web application firewalls can provide additional defense-in-depth layers, while regular security training for administrators helps prevent social engineering attacks that might exploit this vulnerability. The flaw aligns with CWE-79, which specifically addresses cross-site scripting vulnerabilities, and represents a significant concern within the ATT&CK framework under the T1059.001 technique for command and scripting interpreter. Organizations must conduct thorough risk assessments to identify all SharePoint Server instances and ensure comprehensive patch management across their enterprise infrastructure to prevent exploitation of this persistent security weakness.