CVE-2017-11820 in SharePoint Enterprise Server
Summary
by MITRE
Microsoft SharePoint Enterprise Server 2013 SP1 and Microsoft SharePoint Enterprise Server 2016 allow an attacker to exploit a cross-site scripting (XSS) vulnerability by sending a specially crafted request to an affected SharePoint server, due to how SharePoint Server sanitizes web requests, aka "Microsoft Office SharePoint XSS Vulnerability". This CVE ID is unique from CVE-2017-11775 and CVE-2017-11777.
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Analysis
by VulDB Data Team • 01/16/2021
The vulnerability identified as CVE-2017-11820 represents a critical cross-site scripting weakness in Microsoft SharePoint Enterprise Server versions 2013 SP1 and 2016. This security flaw stems from inadequate sanitization of web requests within the SharePoint Server infrastructure, creating an exploitable condition that allows malicious actors to inject harmful scripts into web pages viewed by other users. The vulnerability specifically affects the server's ability to properly filter and validate user input, enabling attackers to bypass security controls that should prevent malicious code execution. The issue manifests when SharePoint Server processes specially crafted requests that contain malicious payloads, which are then rendered in web interfaces without proper sanitization. This particular vulnerability is distinct from related issues CVE-2017-11775 and CVE-2017-11777, each representing separate code paths and exploitation vectors within the SharePoint ecosystem.
The technical implementation of this XSS vulnerability occurs at the input validation layer within SharePoint Server's request processing pipeline. When users submit content or interact with SharePoint interfaces, the server should sanitize all input to prevent script injection attacks. However, in affected versions, certain patterns of user-supplied data are not properly filtered, allowing attackers to embed malicious JavaScript code within URLs, form fields, or other web request parameters. The vulnerability leverages the server's insufficient validation of web requests, particularly affecting areas where SharePoint renders user-provided content without adequate security measures. Attackers can craft malicious URLs or content that, when processed by the SharePoint server, executes scripts in the context of other users' browsers. This creates a persistent threat where compromised users' sessions could be hijacked, sensitive data could be exfiltrated, or malicious commands could be executed on behalf of authenticated users.
The operational impact of CVE-2017-11820 extends beyond simple script execution, potentially enabling attackers to establish persistent access to SharePoint environments and compromise entire organizational networks. An attacker exploiting this vulnerability could gain access to sensitive documents, user credentials, or internal network resources that are protected by SharePoint's access controls. The vulnerability particularly affects organizations that rely heavily on SharePoint for document management, collaboration, and information sharing, as these environments often contain critical business data and personal information. Successful exploitation could lead to data breaches, privilege escalation, and potential lateral movement within the network. The vulnerability's impact is amplified in environments where SharePoint serves as a central hub for enterprise collaboration, as compromised systems could provide attackers with access to multiple interconnected applications and services.
Organizations should implement immediate mitigations including applying the relevant Microsoft security patches released in response to this vulnerability, which address the root cause in SharePoint Server's input validation mechanisms. Network segmentation and web application firewalls can provide additional protection layers to detect and block malicious requests before they reach vulnerable SharePoint servers. Regular monitoring of SharePoint logs for suspicious activity and implementing robust input validation policies can help identify potential exploitation attempts. Security teams should also conduct comprehensive vulnerability assessments to identify all SharePoint installations within their environment and ensure proper patch management procedures are in place. The vulnerability aligns with CWE-79, which specifically addresses cross-site scripting flaws in web applications, and maps to ATT&CK techniques involving command and control through web application exploitation. Organizations should also consider implementing content security policies and ensuring that SharePoint servers properly sanitize all user input through multiple validation layers to prevent similar vulnerabilities from being exploited in the future.