CVE-2026-97779 in Excel
Summary
by MITRE • 10/14/2026
Out-of-bounds read in Microsoft Office Excel allows an unauthorized attacker to disclose information 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 categorized as an out-of-bounds read error. This type of memory corruption issue arises when software attempts to access data stored at a memory location that lies outside the boundaries of the intended buffer or array structure. In the context of Excel, this typically occurs during the parsing and rendering of complex spreadsheet files containing specially crafted formulas, embedded objects, or malformed metadata structures. When an attacker constructs a malicious document designed to exploit these specific edge cases in the application's logic engine, they can trigger the erroneous memory access sequence that leads to the disclosure of sensitive information residing in adjacent memory regions.
From a technical perspective, out-of-bounds reads are particularly dangerous because they allow for non-destructive data exfiltration without necessarily crashing the host system immediately. Unlike buffer overflows which often lead to arbitrary code execution and immediate application termination, an out-of-bounds read provides the attacker with a mechanism to leak internal state information such as stack canaries, heap pointers, or other sensitive variables that may be stored in memory adjacent to the targeted data structure. This capability significantly aids attackers in bypassing modern security mitigations like Address Space Layout Randomization by leaking addresses of critical libraries and functions, thereby facilitating more advanced exploitation chains involving arbitrary code execution. The vulnerability is classified under CWE-125, which defines out-of-bounds read errors as a distinct category of memory safety violations that compromise data confidentiality even if integrity or availability are not immediately impacted.
The operational impact of this vulnerability centers on the unauthorized disclosure of information over a network, implying that an attacker can leverage remote vectors to extract sensitive data from the victim's system. If exploited successfully through a phishing campaign where a user opens a malicious Excel file sent via email or downloaded from a compromised website, the attacker gains the ability to read arbitrary memory contents. This could lead to the exposure of credentials stored in browser caches or password managers if those processes share accessible memory space with Office applications on modern operating systems that utilize shared memory mechanisms for performance optimization. Furthermore, the leaked information can serve as reconnaissance data for subsequent attacks, allowing the adversary to map out the system environment and identify high-value targets within the network infrastructure.
In terms of threat modeling, this vulnerability aligns with ATT&CK technique T1005, which refers to Data from Local System, specifically under sub-techniques related to memory dumping or reading process memory. The attack vector is typically classified as remote via a local application, meaning it requires user interaction such as opening the malicious file but does not require direct network access to the target machine itself beyond delivering the payload. This distinction highlights the importance of endpoint protection strategies that monitor for suspicious behavior patterns associated with memory scraping rather than relying solely on perimeter defenses. Organizations must recognize that even vulnerabilities described primarily as information disclosure can serve as critical stepping stones in complex multi-stage intrusion campaigns.
Mitigation efforts should prioritize immediate patching through official Microsoft security updates, which address the underlying logic errors responsible for the boundary checks failure. Administrators are advised to deploy these patches across all endpoints running vulnerable versions of Office Excel and verify installation success through automated compliance scanning tools. In addition to software remediation, organizations should implement application control policies such as Windows Defender Application Control or AppLocker to restrict the execution of untrusted scripts and macros within Office applications. Enabling Protected View for files originating from the internet can also mitigate risk by isolating potentially malicious documents in a sandboxed environment where memory access is restricted. User awareness training remains essential, emphasizing caution when opening attachments from unknown sources and verifying sender authenticity before interaction. Regular vulnerability assessments and penetration testing should be conducted to identify similar weaknesses in custom macros or add-ins that may bypass standard security controls.