CVE-2026-55058 in Excel
Summary
by MITRE • 07/14/2026
Out-of-bounds read in Microsoft Office Excel allows an unauthorized attacker to execute code locally.
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Analysis
by VulDB Data Team • 07/15/2026
This vulnerability represents a critical security flaw in Microsoft Office Excel that stems from improper input validation during the processing of malformed spreadsheet files. The out-of-bounds read condition occurs when Excel attempts to parse specific data structures within workbook files without adequate bounds checking, allowing an attacker to manipulate memory access patterns that exceed allocated buffer boundaries. Such flaws typically arise from insufficient validation of user-supplied data in spreadsheet formats including xlsx, xls, or other Microsoft Office document variants. The vulnerability aligns with CWE-129, which specifically addresses inadequate bounds checking in input validation scenarios, and may also relate to CWE-787 when the out-of-bounds access results in memory corruption that can be exploited for code execution. From an operational perspective, this vulnerability presents a significant risk as it enables remote code execution through social engineering attacks where victims open maliciously crafted Excel files. Attackers can leverage this weakness by constructing specially formatted spreadsheet documents that trigger the vulnerable code path when opened by an affected version of Excel, potentially allowing arbitrary code execution with the privileges of the victim user. The attack surface is particularly concerning given Excel's widespread use across enterprise environments and the common practice of opening email attachments or files from untrusted sources. The exploitation typically follows ATT&CK technique T1059.005 for Windows Command Shell execution, where attackers may chain this vulnerability with additional payload delivery mechanisms to establish persistent access or escalate privileges within compromised systems. Organizations should prioritize immediate patching of affected Excel versions and implement strict file validation policies that prevent the opening of untrusted spreadsheet files. Additional mitigations include deploying application whitelisting solutions, configuring Microsoft Office to disable automatic execution of macros, and establishing network-based controls to filter potentially malicious Office document formats at perimeter defenses. Security teams should also monitor for indicators of compromise related to suspicious Excel file access patterns and consider implementing sandboxing technologies for processing untrusted Office documents in isolated environments. The vulnerability demonstrates the critical importance of input validation in office productivity software and highlights how seemingly benign file format parsing can become a gateway for sophisticated attack chains involving privilege escalation and persistent threat operations.