CVE-2026-97753 in Excel
Summary
by MITRE • 10/14/2026
Heap-based buffer overflow in Microsoft Office Excel allows an unauthorized attacker to execute code over a network.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability described constitutes a critical security flaw within the Microsoft Office Excel application, specifically manifesting as a heap-based buffer overflow. This type of memory corruption error occurs when a program writes data beyond the allocated boundaries of a buffer located in the computer's random access memory, known as the heap. In the context of Excel, this typically happens during the processing of specially crafted files or external inputs that trigger malformed parsing routines within the application’s core engine. The attacker leverages this flaw to overwrite adjacent memory structures with malicious shellcode or control flow hijacking data, thereby gaining the ability to execute arbitrary code on the victim's system. Because Microsoft Office applications are frequently used in enterprise environments where documents are shared via email and network shares, the attack vector is predominantly remote, allowing an unauthorized attacker to exploit this weakness over a network without requiring physical access or prior authentication to the target machine.
From a technical perspective, heap-based buffer overflows differ from stack-based ones in that they affect dynamically allocated memory regions used during runtime execution. When Excel processes certain file formats such as XLSX, XLTM, or other legacy binary formats containing embedded objects, scripts, or complex formulas, it may fail to properly validate the length of input data against the size of the destination buffer. This lack of bounds checking allows an attacker to craft a malicious document that, when opened by the user, causes Excel to write more data than intended into the heap space. By carefully controlling this overflow, the attacker can manipulate function pointers or exception handlers within the application’s memory layout. Once these control structures are overwritten with addresses pointing to injected payload code, the processor redirects execution flow to the malicious instructions upon encountering specific triggers, such as closing the document or triggering a particular calculation event. This mechanism effectively bypasses standard user-level restrictions and grants the attacker full administrative privileges on the compromised system, depending on the privilege level under which Excel is running.
The operational impact of this vulnerability is severe due to its potential for widespread exploitation in corporate networks. Since Microsoft Office remains a ubiquitous tool across industries, any unpatched endpoint becomes an attractive target for automated scanning tools and targeted attacks alike. Successful exploitation allows adversaries to establish persistent access, install backdoors, exfiltrate sensitive data, or pivot further into the internal network by leveraging the compromised machine as a foothold. The remote nature of this exploit means that social engineering tactics such as phishing emails with malicious attachments are highly effective delivery mechanisms. Users who open these files inadvertently initiate the exploitation chain, leading to complete system compromise without any additional interaction required beyond opening and potentially closing the document. This high ease of use combined with broad applicability makes it a priority target for advanced persistent threat groups seeking initial access vectors within organizational perimeters.
To mitigate this risk, organizations must prioritize immediate patching through Microsoft’s official update channels, ensuring that all instances of Office Excel are updated to versions containing fixes for heap validation errors in file parsing routines. Security teams should also implement application control policies using technologies like Windows Defender Application Control or AppLocker to restrict the execution of untrusted scripts and binaries generated by office applications. Additionally, enabling Protected View for files originating from uncertain sources can isolate potentially malicious content within a sandboxed environment, preventing direct interaction with system resources. Network segmentation strategies further limit lateral movement if an endpoint is compromised, while user awareness training helps reduce the success rate of phishing campaigns that deliver these exploit payloads. Regular vulnerability assessments and penetration testing should be conducted to identify misconfigurations or outdated software versions that remain exposed to such high-severity flaws aligned with CWE-122 for heap-based buffer overflows and MITRE ATT&CK technique T1059 for command and script interpretation via Office macros or embedded objects.