CVE-2026-55131 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 in Microsoft Office Excel that enables remote code execution when a malicious file is opened by an unsuspecting user. This critical flaw resides in the application's handling of malformed spreadsheet files, specifically within the memory management routines responsible for processing various data structures. The vulnerability manifests when Excel attempts to allocate memory on the heap for processing crafted data elements that exceed predetermined buffer boundaries. Attackers can exploit this condition by constructing specially formatted excel files containing oversized data arrays or malformed records that trigger the overflow during parsing operations.
The technical implementation of this vulnerability leverages improper input validation mechanisms within Excel's spreadsheet engine, where the application fails to adequately verify the size and structure of incoming data before attempting memory allocation. When processing maliciously crafted cells, formulas, or embedded objects, the software allocates insufficient heap space for data storage, creating a condition where subsequent writes overflow into adjacent memory regions. This overflow can overwrite critical program execution pointers, return addresses, or other control data structures that govern the application's operational flow.
The operational impact of this vulnerability extends beyond simple local privilege escalation as it provides attackers with a reliable method for executing arbitrary code within the context of the targeted user's session. Once successfully exploited, the attacker gains complete control over the victim's system, potentially enabling data exfiltration, persistence mechanisms, or further lateral movement within the network. The attack vector requires only social engineering to convince users to open malicious files, making it particularly dangerous in enterprise environments where users frequently interact with spreadsheet documents from external sources.
This vulnerability aligns with CWE-121 heap-based buffer overflow classification and maps directly to attack techniques described in the MITRE ATT&CK framework under initial access and execution phases. The exploitation typically follows a pattern of phishing campaigns delivering malicious excel files through email attachments or compromised websites, leveraging the trust users place in common office applications. Security professionals should consider implementing multiple layers of defense including application whitelisting policies that restrict execution of untrusted files, regular security updates to patch known vulnerabilities, and user education programs to recognize suspicious file attachments. Network-based intrusion detection systems can also help identify anomalous behavior patterns associated with exploitation attempts, while endpoint protection solutions should be configured to monitor for unusual memory allocation patterns or process behavior indicative of buffer overflow conditions.
Organizations should prioritize immediate remediation through Microsoft's security updates and patches addressing this vulnerability, while simultaneously implementing network segmentation controls to limit lateral movement capabilities once an attacker gains initial access. Regular security assessments should include testing for similar vulnerabilities in other office applications and third-party software components that may present comparable attack surfaces. The remediation process must account for both immediate patch deployment and long-term security architecture improvements to prevent similar vulnerabilities from emerging in future software releases or configurations.