CVE-2026-88163 in SharePoint Server
Summary
by MITRE • 10/14/2026
Integer overflow or wraparound in Microsoft Office SharePoint allows an authorized attacker to execute code over a network.
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Analysis
by VulDB Data Team • 10/15/2026
The vulnerability described involves a critical integer overflow or wraparound flaw within the core processing logic of Microsoft Office SharePoint Server, specifically affecting components responsible for handling data structures during document parsing and rendering operations. This type of memory corruption error occurs when an arithmetic operation produces a result that exceeds the maximum value representable by the allocated integer variable, causing it to wrap around to a small negative or zero value rather than throwing an exception. In the context of SharePoint, this flaw is typically triggered when processing specially crafted Office documents such as Word files, Excel spreadsheets, or PowerPoint presentations uploaded through web interfaces or accessed via standard network protocols like HTTP and SMB. The vulnerability allows for arbitrary code execution because the miscalculated size values lead to improper memory allocation decisions by the underlying operating system libraries, resulting in buffer overflows that can be exploited to overwrite adjacent memory structures including return addresses on the stack or function pointers in heap metadata.
From a technical perspective, this flaw aligns with CWE-190 Integer Overflow or Wraparound and often serves as the precursor for CWE-120 Buffer Copy without Checking Size of Input Classic Buffer Overflow. The exploitation mechanism relies on precise control over input data to manipulate internal counters used during memory allocation routines within SharePoint's document conversion engine or rendering pipeline. When an authorized user, such as a site collection administrator or any authenticated user with upload privileges depending on the specific version and configuration, submits a maliciously crafted file, the application processes it without adequate bounds checking. The integer overflow causes the system to allocate significantly less memory than required for the actual data payload. Subsequent writes into this undersized buffer overwrite critical control structures in adjacent memory regions, allowing an attacker to redirect execution flow to shellcode injected within the same request or loaded via secondary vectors such as DLL hijacking if applicable permissions exist.
The operational impact of this vulnerability is severe due to its potential for remote code execution with elevated privileges depending on the service account context under which SharePoint runs. Since authentication is required, it does not qualify as a fully unauthenticated zero-day but remains highly dangerous in environments where internal users may be tricked into opening malicious documents or when automated processes process external inputs without strict validation. Successful exploitation grants an attacker full control over the affected server instance, enabling them to install backdoors, steal sensitive data stored within SharePoint libraries, pivot to other systems on the network using harvested credentials, and modify system configurations. This compromises the confidentiality, integrity, and availability of enterprise information assets managed by the platform.
Mitigation strategies must focus on both immediate remediation and long-term architectural hardening. The primary defense is applying the latest security updates provided by Microsoft that patch this specific integer overflow condition within SharePoint binaries. Organizations should ensure all servers are running supported versions with cumulative updates applied regularly to address known vulnerabilities in document processing components. Additionally, implementing strict input validation policies at the application layer can help detect malformed files before they reach vulnerable parsers. Network segmentation and firewall rules restricting access to SharePoint services from untrusted networks reduce the attack surface for authenticated attackers who might exploit this flaw remotely. Security awareness training is also crucial to prevent social engineering attacks that lead users to open malicious documents, while endpoint detection and response solutions should be configured to monitor for anomalous process creation patterns indicative of exploitation attempts such as unexpected spawning of command shells from Office applications or SharePoint services.