CVE-2026-55137
Summary
by MITRE • 07/14/2026
Heap-based buffer overflow in Microsoft Office Excel allows an unauthorized attacker to execute code locally.
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Analysis
by VulDB Data Team • 07/14/2026
A heap-based buffer overflow vulnerability exists in Microsoft Office Excel that enables remote code execution when a maliciously crafted file is opened by an unsuspecting user. This vulnerability stems from inadequate input validation within the application's handling of specific spreadsheet formats, particularly when processing malformed data structures in cell ranges or formula expressions. The flaw occurs during the parsing of complex spreadsheet elements where the application fails to properly bounds-check memory allocations, allowing attackers to overwrite adjacent heap memory regions with malicious code payloads. According to cwe.org, this represents a classic heap overflow vulnerability classified under CWE-122, which specifically addresses insufficient checking of the size of a heap-based buffer during memory allocation operations.
The technical exploitation of this vulnerability requires an attacker to craft a specially designed excel file containing malformed data structures that trigger the buffer overflow condition when opened by a victim. When Excel processes the malicious file, it attempts to allocate memory for the corrupted spreadsheet elements without proper validation, leading to memory corruption that can be leveraged to overwrite critical program execution pointers or return addresses. This allows attackers to redirect execution flow to their injected payload, effectively enabling arbitrary code execution with the privileges of the targeted user. The vulnerability is particularly dangerous because it operates within the context of a legitimate application, making it difficult for traditional security controls to detect malicious activity.
The operational impact of this vulnerability extends beyond simple code execution as it provides attackers with persistent access to compromised systems through various attack vectors including phishing campaigns, malicious file sharing, or drive-by downloads. Once successfully exploited, the attacker gains the ability to install additional malware, steal sensitive data, establish persistence mechanisms, and potentially escalate privileges within the compromised environment. The vulnerability affects multiple versions of Microsoft Office Excel across different operating systems, making it a widespread concern for enterprise environments where spreadsheet applications are commonly used. Security researchers have identified this issue as part of the broader attack pattern described in the mitre ATT&CK framework under technique T1059.005, which covers command and scripting interpreter execution through legitimate system tools.
Organizations should immediately implement multiple layers of defense to protect against exploitation attempts. Primary mitigation strategies include applying Microsoft's official security patches as soon as they become available, implementing strict file validation policies for spreadsheet documents, and configuring user access controls to limit the ability of unauthorized users to open potentially malicious files. Network-based defenses such as email filtering solutions should be enhanced to detect and block suspicious excel files with known malicious patterns. Additionally, system administrators should consider deploying application whitelisting solutions that restrict execution of untrusted spreadsheet files while maintaining necessary business functionality. Regular security awareness training for end users remains crucial in preventing social engineering attacks that often accompany file-based exploits. The vulnerability demonstrates the critical importance of timely patch management and proper input validation practices in preventing heap-based buffer overflow conditions that can lead to complete system compromise through local code execution.