CVE-2020-1099 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 CVE ID is unique from CVE-2020-1100, CVE-2020-1101, CVE-2020-1106.
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Analysis
by VulDB Data Team • 02/28/2025
The vulnerability identified as CVE-2020-1099 represents a critical cross-site scripting flaw within Microsoft SharePoint Server that arises from inadequate input sanitization mechanisms. This security weakness specifically manifests when the affected SharePoint server fails to properly process and sanitize maliciously crafted web requests, creating an exploitable condition that allows attackers to inject malicious scripts into web pages viewed by other users. The vulnerability operates at the application layer where user-supplied input is not sufficiently validated or escaped before being rendered in web responses, making it particularly dangerous in collaborative environments where SharePoint servers host sensitive organizational data and user interactions.
The technical implementation of this XSS vulnerability stems from Microsoft SharePoint Server's insufficient validation of user input parameters within web requests. When a malicious actor crafts a specially designed HTTP request containing script payloads, the server processes this input without adequate sanitization measures that would normally prevent execution of unauthorized code. This flaw typically occurs in areas where SharePoint renders user-generated content or processes parameters from URL queries, form submissions, or other input vectors that are not properly escaped or validated against known malicious patterns. The vulnerability's classification as a reflected XSS issue means that malicious scripts are executed in the context of other users' browsers, potentially allowing attackers to access sensitive session information, steal credentials, or perform unauthorized actions on behalf of victims.
The operational impact of CVE-2020-1099 extends beyond simple script execution, as it provides attackers with potential access to sensitive organizational data and system functionality within SharePoint environments. An attacker could leverage this vulnerability to establish persistent access through session hijacking, execute malicious code in users' browsers, or redirect victims to phishing sites that appear legitimate. The attack surface is particularly concerning in enterprise environments where SharePoint servers often contain confidential business information, employee records, and internal communications that could be compromised. Additionally, the vulnerability's presence in Microsoft Office SharePoint Server creates cascading risks as attackers may use the initial compromise to escalate privileges or move laterally within the network infrastructure, potentially affecting other connected systems and services.
Organizations affected by this vulnerability should implement immediate mitigations including applying Microsoft's security patches and updates, implementing robust input validation mechanisms, and deploying web application firewalls to filter malicious requests. The vulnerability aligns with CWE-79 which specifically addresses cross-site scripting flaws in software applications, and its exploitation patterns correspond to techniques documented in the ATT&CK framework under the T1059.001 technique for command and scripting interpreter. Security teams should also consider implementing content security policies, enabling proper output encoding for all user-supplied data, and conducting regular security assessments to identify and remediate similar input validation weaknesses. Network segmentation and monitoring solutions should be enhanced to detect anomalous traffic patterns that may indicate exploitation attempts, while user education programs should emphasize recognizing and reporting suspicious SharePoint interactions that could indicate an active attack.