CVE-2026-56156
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 critical security flaw resides within the application's handling of specific data structures during file processing, particularly when parsing malformed or specially constructed spreadsheet elements. The vulnerability stems from insufficient bounds checking mechanisms that fail to validate the size of data being written to heap-allocated memory regions, creating opportunities for attackers to overwrite adjacent memory locations with malicious code payloads.
The technical implementation of this vulnerability involves the exploitation of improper memory management practices within Excel's internal parsing routines. When processing certain spreadsheet formats or embedded objects, the application allocates memory on the heap without adequate validation of input data sizes, allowing an attacker to craft input that exceeds allocated buffer boundaries. This overflow can corrupt critical heap metadata structures and potentially overwrite function pointers or return addresses, enabling arbitrary code execution with the privileges of the targeted user. The vulnerability is particularly dangerous because it requires no special privileges to exploit and can be delivered through email attachments or malicious documents.
The operational impact of this vulnerability extends beyond simple local privilege escalation, as it represents a significant threat vector for phishing campaigns and social engineering attacks. Attackers can craft specially designed excel files that appear legitimate but contain malicious code designed to exploit the buffer overflow when opened by victims. Once executed, the malicious payload can establish persistence, exfiltrate sensitive data, or provide remote access capabilities to the compromised system. The vulnerability affects multiple versions of Microsoft Office Excel across different operating systems and presents a substantial risk to enterprise environments where users frequently open spreadsheet files from untrusted sources.
Security professionals should implement layered mitigation strategies including regular patching of affected Microsoft Office versions, deployment of application whitelisting solutions, and enhanced email filtering to prevent delivery of malicious documents. Network segmentation and endpoint protection mechanisms can help limit the potential impact if exploitation occurs. Organizations should also consider implementing user education programs to reduce the likelihood of users opening suspicious spreadsheet files. The vulnerability aligns with attack patterns documented in the mitre ATT&CK framework under techniques related to initial access through malicious files and privilege escalation through code execution. According to CWE classification, this represents a classic heap-based buffer overflow vulnerability (CWE-122) that falls under the broader category of memory safety issues affecting application security.