CVE-2026-55053 in Office
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 • 07/15/2026
A heap-based buffer overflow vulnerability exists within Microsoft Office Excel that enables remote code execution when a maliciously crafted file is opened by an unsuspecting user. This critical security flaw resides in the application's handling of malformed data structures during spreadsheet processing, specifically when parsing certain cell formats or embedded objects within excel files. The vulnerability stems from insufficient bounds checking mechanisms that fail to validate the size of data allocated on the heap memory space before writing additional information into allocated buffers.
The technical implementation of this vulnerability involves an attacker crafting a specially designed excel file containing malformed data structures that trigger memory corruption when processed by the vulnerable application. When Excel attempts to parse these malicious elements, it allocates insufficient memory space for data storage and subsequently writes beyond the allocated buffer boundaries into adjacent heap memory regions. This memory corruption can overwrite critical program execution pointers or control data structures, allowing an attacker to manipulate the program flow and execute arbitrary code with the privileges of the targeted user.
The operational impact of this vulnerability extends beyond simple local privilege escalation as it provides attackers with a powerful vector for initial system compromise through social engineering campaigns targeting office environments. Attackers can distribute malicious excel files via email phishing campaigns or compromised websites, where unsuspecting users inadvertently open the files and trigger the exploit. The vulnerability is particularly dangerous because it operates within the trusted application context of Microsoft Office, making detection more challenging for traditional security controls that focus on network-level threats rather than application-level memory corruption.
Security researchers have classified this vulnerability under common weakness enumeration as CWE-121 heap-based buffer overflow, which represents a fundamental flaw in memory management practices where insufficient validation allows data to overwrite adjacent memory locations. The attack pattern aligns with ATT&CK technique T1059 005 for command and scripting interpreter using excel applications as the initial access vector, potentially leading to further compromise through privilege escalation or lateral movement within the network environment. Organizations should implement immediate mitigations including disabling macro execution in office applications, implementing strict file validation policies, and ensuring timely patch deployment for affected versions of Microsoft Office.
The exploitability of this vulnerability requires minimal user interaction beyond opening the malicious file, making it particularly dangerous in enterprise environments where users frequently interact with external documents. Network segmentation and email filtering solutions can help reduce the risk but cannot completely eliminate the threat without proper application-level defenses. Organizations should also consider implementing application whitelisting policies to restrict execution of unauthorized office applications or plugins that may be leveraged as secondary attack vectors. Regular security awareness training for end users remains crucial in defending against social engineering components of these attacks, as the human element continues to represent the most significant weakness in many security frameworks.