CVE-2026-81949 in Excel
Summary
by MITRE • 09/09/2026
Integer overflow or wraparound in Microsoft Office Excel allows an unauthorized attacker to execute code locally.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability described involves a critical integer overflow condition within the core processing engine of Microsoft Office Excel, specifically affecting how certain data structures and memory allocations are handled during file parsing operations. This flaw stems from inadequate validation checks on numeric values derived from user-supplied input embedded in spreadsheet files or related artifacts processed by the application. When an attacker crafts a malicious document containing specially constructed numerical inputs that exceed expected bounds, the internal arithmetic logic fails to account for the resulting overflow, leading to incorrect calculations regarding memory buffer sizes. This miscalculation typically results in the allocation of significantly smaller buffers than required for storing subsequent data structures or processing operations.
From a technical perspective, this integer wraparound represents a classic CWE-190 vulnerability type where signed integers are used when unsigned ones would be more appropriate, or where bounds checking is omitted before arithmetic operations that can exceed maximum limits. The exploitation of this flaw allows an unauthorized attacker to achieve arbitrary code execution on the local system with the privileges of the currently logged-in user. By triggering the overflow during the parsing phase, the attacker can manipulate heap memory layouts, potentially overwriting critical control data such as function pointers or exception handlers. This mechanism facilitates a buffer overflow scenario that grants the adversary full control over program flow, enabling them to inject and execute shellcode within the context of the Excel process.
The operational impact of this vulnerability is severe due to its potential for remote exploitation if delivered via phishing campaigns involving malicious attachments. An attacker can distribute a crafted Excel file through email or network shares, relying on social engineering to induce a victim to open it. Once opened, the exploit triggers automatically during the parsing routine without requiring further user interaction in many scenarios. This leads to complete compromise of the workstation, allowing for data exfiltration, installation of persistent backdoors, lateral movement within corporate networks, and potential escalation to system-level privileges depending on configuration settings like User Account Control states. The attack aligns with MITRE ATT&CK techniques related to initial access via spearphishing attachment and execution through command scripting or binary exploitation.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. Organizations should immediately apply the latest security patches released by Microsoft for all versions of Office Excel affected by this vulnerability, ensuring that update cycles are strictly adhered to across endpoints. Security teams should also implement application whitelisting policies to restrict execution of untrusted scripts or binaries spawned from office applications, thereby limiting post-exploitation capabilities even if an exploit succeeds. Additionally, deploying advanced endpoint detection and response solutions can help identify anomalous behavior patterns associated with memory corruption exploits, such as unusual heap allocations or attempts to modify executable memory regions. User awareness training remains crucial to reduce the likelihood of successful social engineering attacks that serve as the delivery vector for this vulnerability.