CVE-2026-88166 in SharePoint
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 • 10/14/2026
The vulnerability described involves a critical integer overflow condition within the core processing logic of Microsoft Office SharePoint, specifically affecting components responsible for handling data structures that rely on precise memory allocation and boundary checks. This flaw arises when the application fails to properly validate arithmetic operations involving user-supplied input or internal state variables before performing calculations related to buffer sizes or array indices. When an integer value exceeds its maximum representable limit during such a calculation, it wraps around to a small negative number or a significantly smaller positive value than intended. In systems programming and software architecture, this wraparound behavior is particularly dangerous because subsequent memory allocation routines often rely on these calculated values to determine the size of buffers required for processing incoming data. Consequently, if the overflow results in an underestimation of the necessary buffer size, the system allocates a block of memory that is insufficient to hold the actual input payload provided by the attacker.
This discrepancy between allocated and expected memory sizes creates a classic heap-based or stack-based buffer overflow scenario, depending on where the vulnerable operation occurs within SharePoint's execution context. An authorized attacker can exploit this condition by crafting specific network requests containing maliciously formatted data that triggers the integer arithmetic error. By carefully controlling the input values to induce the wraparound, the attacker ensures that the subsequent write operations exceed the bounds of the allocated buffer. This out-of-bounds memory access allows for arbitrary code execution on the target server or client machine where SharePoint is running. The severity of this vulnerability is compounded by its network-exploitable nature and the fact that it requires only authorized authentication to trigger, meaning any user with valid credentials can potentially compromise the integrity of the entire system.
From a threat modeling perspective, this flaw aligns closely with CWE-190, which defines integer overflow or wraparound as a weakness where arithmetic operations produce results too large for the data type used. Furthermore, in terms of attack vectors and tactics, this vulnerability maps to MITRE ATT&CK technique T1203, specifically exploitation for code execution via buffer overflows. The operational impact is severe, as successful exploitation grants the attacker full control over the affected process with the privileges of the SharePoint service account or user context. This can lead to complete system compromise, including data exfiltration, installation of backdoors, lateral movement within the network, and disruption of critical business services hosted on the platform. The ability to execute code remotely via a network connection makes this an high-priority target for automated scanning tools and advanced persistent threat actors seeking initial access points in enterprise environments.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. Microsoft has released security updates that patch these specific integer overflow conditions by implementing stricter input validation, enhanced boundary checks, and safer arithmetic operations within the SharePoint codebase. Organizations should prioritize applying the latest cumulative updates or standalone patches provided by Microsoft to all affected versions of Office SharePoint Server. Additionally, network segmentation can help limit exposure by restricting access to SharePoint services only from trusted subnets and enforcing strict authentication policies using multi-factor authentication where possible. Developers involved in custom integrations with SharePoint should also review their code for similar patterns, ensuring that any data passed through web services or APIs undergoes rigorous validation before being processed by underlying system libraries. Regular vulnerability assessments and penetration testing are essential to identify residual risks and ensure that the patched environment remains resilient against evolving exploitation techniques.