CVE-2026-81393
Summary
by MITRE • 09/08/2026
Out-of-bounds read in Microsoft Office Excel allows an unauthorized attacker to disclose information locally.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability described constitutes a critical security flaw within the Microsoft Office Excel application, specifically categorized as an out-of-bounds read error. This type of memory corruption issue arises when software attempts to access data stored at a memory location that is outside the boundaries of the intended buffer or array structure. In the context of Excel, this typically occurs during the parsing and rendering of complex spreadsheet files containing specially crafted formulas, macros, or embedded objects. When an attacker constructs a malicious document designed to exploit this specific logic error in the application's codebase, they can trigger the unauthorized reading of memory contents that were not intended for public access. This flaw is fundamentally rooted in improper boundary checks within the data processing routines, allowing execution flow to continue despite accessing invalid memory addresses rather than terminating safely as secure coding practices would dictate.
From a technical perspective, this vulnerability aligns with Common Weakness Enumeration (CWE) identifiers such as CWE-125, which defines out-of-bounds read vulnerabilities where an application reads data past the end or before the beginning of the intended buffer. The operational impact of exploiting this flaw is primarily centered on information disclosure rather than immediate code execution or system compromise. By leveraging this weakness, a local attacker can potentially extract sensitive data from the process memory space of Excel. This may include cached credentials, previously opened document contents, clipboard history, or other proprietary information residing in adjacent memory blocks. While the initial vector requires user interaction to open the malicious file locally, the resulting exposure of internal application state poses significant risks to confidentiality and integrity within an enterprise environment where sensitive financial data or intellectual property is frequently processed through spreadsheets.
The attack scenario generally involves social engineering tactics wherein a victim is persuaded to open a specially crafted Excel file from an untrusted source. Once opened, the malicious payload triggers the out-of-bounds read condition during the document's initialization phase. The attacker does not need administrative privileges on the target system because the vulnerability exists within the user-level application process itself. However, the scope of data exfiltration is limited to what resides in the memory space accessible by that specific Excel instance at the time of exploitation. This limitation distinguishes it from more severe vulnerabilities like remote code execution flaws, yet its prevalence and ease of exploitation make it a persistent threat vector for targeted attacks aiming at corporate espionage or credential harvesting.
Mitigation strategies must address both immediate remediation and long-term defensive posture improvements. The most effective countermeasure is the timely application of security updates provided by Microsoft through Windows Update or the Office update channel, which patch the underlying memory management logic to enforce strict boundary checks. Organizations should prioritize deploying these patches across all endpoints running affected versions of Excel. Additionally implementing application control policies such as AppLocker or Windows Defender Application Control can restrict the execution of untrusted scripts and macros often associated with delivering exploits for this vulnerability. Users must be educated on recognizing suspicious file attachments and avoiding opening documents from unknown sources. Furthermore, enabling Enhanced Security Configuration in Office applications adds an additional layer of protection by restricting macro functionality by default, thereby reducing the attack surface available to adversaries attempting to leverage such memory corruption flaws for information disclosure purposes.