CVE-2026-97747 in Excel
Summary
by MITRE • 10/14/2026
Use after free 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 involves a use-after-free condition within the core processing engine of Microsoft Office Excel, specifically affecting components responsible for parsing and rendering spreadsheet data structures. This class of memory corruption flaw occurs when software continues to use pointers that have already been freed from dynamic memory allocation. In the context of Excel, this typically manifests during the handling of complex or malformed document files where internal objects are deallocated but subsequent operations attempt to access their previously allocated memory space. Because Microsoft Office applications process untrusted data formats such as .xlsx and .xls files which can be downloaded via email attachments or accessed through network shares, an attacker who successfully exploits this flaw gains the ability to execute arbitrary code on a targeted system over a network without requiring user interaction beyond opening the malicious file.
From a technical perspective, use-after-free vulnerabilities are particularly dangerous because they allow attackers to manipulate memory layout and control execution flow with high precision. When Excel attempts to access freed memory, it may read stale data or write to unintended locations depending on how the heap has been reallocated in the interim. An attacker can craft a specially designed spreadsheet file that triggers this condition during parsing of specific formulas, embedded objects, or formatting rules. By carefully controlling the contents written into the reused memory region, an adversary can achieve arbitrary code execution, effectively taking control of the application process and potentially the underlying operating system. This aligns with CWE-416 which defines use-after-free as a critical weakness in software development that leads to unpredictable behavior and security breaches.
The operational impact of this vulnerability is severe due to its remote exploitability vector. Since Excel files are commonly exchanged across organizational boundaries via email, instant messaging platforms, or cloud storage services linked through network protocols, the attack surface is extensive. A successful exploitation does not necessarily require elevated privileges on the target machine if the user runs with standard credentials, as many Office applications operate in a context that allows significant system interaction once code execution is achieved. This can lead to full system compromise including data exfiltration, installation of additional malware such as ransomware or backdoors, and lateral movement within internal networks. The ability to execute code over the network makes this vulnerability particularly attractive for automated worm-like propagation campaigns targeting organizations with high volumes of external document exchange.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. Organizations should immediately apply available security patches from Microsoft that address the memory management logic within Excel’s parsing routines. It is critical to ensure that all endpoints running vulnerable versions of Office are updated promptly as these updates often include specific checks for malformed structures that trigger use-after-free conditions. Additionally, implementing application control policies such as Windows Defender Application Control or AppLocker can restrict the execution of untrusted scripts and binaries launched by Office applications, thereby limiting the impact even if exploitation occurs. Network segmentation should be employed to isolate file servers from critical infrastructure, reducing the blast radius in case a compromised workstation attempts lateral movement.
Defensive measures should also include enabling macro security settings to prevent automatic execution of VBA code embedded within documents unless explicitly trusted by the user. While this vulnerability is primarily triggered through native Excel parsing rather than macros alone, many exploitation chains combine multiple techniques including script injection or ActiveX controls which can be mitigated by strict policy enforcement. Security awareness training for employees regarding phishing attempts and suspicious file attachments remains a vital layer of defense since social engineering often precedes the delivery of malicious documents. Furthermore, deploying endpoint detection and response solutions capable of monitoring memory access patterns can help identify anomalous behavior indicative of heap exploitation attempts in real time.
This vulnerability is categorized under ATT&CK technique T1203 which covers exploitation for client execution, highlighting how attackers leverage software vulnerabilities to gain initial access on target systems. The specific nature of the flaw falls squarely within CWE-416 and often intersects with CWE-787 out-of-bounds write if the freed memory is overwritten during the exploit process. Understanding these classifications helps security teams prioritize patching efforts based on industry-standard risk frameworks. Continuous monitoring for indicators of compromise related to Office application behavior, such as unusual network connections initiated by excel.exe or unexpected child processes spawned from it, provides an additional layer of detection against active exploitation attempts in enterprise environments.