CVE-2021-31173 in SharePoint Server
Summary
by MITRE • 05/12/2021
Microsoft SharePoint Server Information Disclosure Vulnerability
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Analysis
by VulDB Data Team • 02/28/2025
The CVE-2021-31173 vulnerability represents a critical information disclosure flaw in Microsoft SharePoint Server that allows unauthenticated attackers to access sensitive data through crafted requests. This vulnerability specifically affects SharePoint Server 2016 and SharePoint Server 2019 installations, where improper input validation enables malicious actors to retrieve information that should remain restricted to authorized users only. The flaw stems from insufficient sanitization of user-supplied input within the SharePoint server-side processing mechanisms, creating an avenue for unauthorized data exposure.
The technical implementation of this vulnerability occurs within the SharePoint Server's request handling pipeline where certain API endpoints fail to properly validate and sanitize incoming parameters. Attackers can exploit this by crafting specially formatted requests that bypass normal authentication and authorization checks, allowing them to access internal SharePoint server information including file paths, system configurations, and potentially user data. The vulnerability operates at the application layer and can be leveraged without requiring any valid credentials or authentication tokens, making it particularly dangerous for organizations with insufficient network segmentation or monitoring controls.
From an operational impact perspective, this vulnerability poses significant risks to organizations relying on SharePoint Server for document management and collaboration. The information disclosure can potentially expose sensitive business data, internal network structures, and system configurations that attackers could use for further exploitation. Security professionals have noted that the vulnerability can be combined with other attack vectors to escalate privileges or gain deeper access to affected systems, creating a potential pathway for more severe compromise scenarios. The lack of authentication requirements means that any attacker with network access can potentially exploit this vulnerability without additional prerequisites.
Organizations should implement immediate mitigations including applying the relevant Microsoft security patches released in the June 2021 security updates, which address the root cause by strengthening input validation and sanitization processes within SharePoint Server. Network segmentation strategies should be reinforced to limit access to SharePoint servers, particularly ensuring that only necessary internal systems can reach these vulnerable endpoints. Additionally, implementing robust monitoring and logging controls around SharePoint server access patterns can help detect anomalous requests that may indicate exploitation attempts. The vulnerability aligns with CWE-20: Improper Input Validation and can be categorized under ATT&CK technique T1083: File and Directory Discovery, making it a significant concern for organizations following standard security frameworks and threat modeling approaches.