CVE-2026-55054 in Office
Summary
by MITRE • 07/14/2026
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 • 07/15/2026
This vulnerability represents a critical out-of-bounds read flaw in Microsoft Office Excel that enables remote attackers to extract sensitive information from affected systems. The vulnerability occurs when Excel processes specially crafted spreadsheet files, leading to memory access violations that can be exploited to disclose confidential data across network connections. Such issues typically arise from insufficient input validation and boundary checking mechanisms within the spreadsheet parsing engine. The technical implementation involves memory corruption patterns where the application attempts to read data beyond allocated buffer boundaries, potentially exposing adjacent memory contents including credentials, encryption keys, or other sensitive information. This type of vulnerability aligns with common weakness enumerations such as CWE-125, which describes out-of-bounds read conditions in software applications. From an operational perspective, attackers can leverage this vulnerability by crafting malicious excel files that, when opened by victims, trigger the memory access violation and subsequently transmit leaked data to attacker-controlled systems. The attack vector operates over network protocols since many users open spreadsheet files directly from web-based sources or email attachments without proper sandboxing measures. This vulnerability also maps to ATT&CK technique T1059 where adversaries use legitimate system processes to execute malicious code, though in this case the exploitation occurs through normal application functionality rather than direct code injection. Organizations running affected Excel versions face significant risks including data breaches, intellectual property theft, and potential lateral movement within networks. The impact extends beyond simple information disclosure as leaked memory contents may contain cryptographic material that could compromise entire security infrastructures. Security professionals should note that this vulnerability often requires user interaction to exploit successfully since users must open the malicious file, making it a prime candidate for social engineering campaigns. Microsoft typically addresses such vulnerabilities through security updates that enhance input validation and memory management controls within the application's spreadsheet processing modules.
The vulnerability demonstrates how seemingly routine office applications can contain complex memory management flaws that have far-reaching security implications. When Excel encounters malformed data structures in spreadsheet files, it fails to properly validate array indices or buffer limits before accessing memory locations, creating opportunities for attackers to manipulate these access patterns and extract unintended information. The network-based nature of the exploitation suggests that organizations should implement network monitoring solutions to detect unusual data exfiltration patterns that might indicate successful exploitation attempts. This type of out-of-bounds read vulnerability represents a fundamental flaw in software security architecture where proper bounds checking mechanisms are either missing or insufficiently implemented. The attack surface expands significantly when considering that many users regularly open spreadsheet files from untrusted sources, making this vulnerability particularly dangerous in enterprise environments where sensitive data is frequently processed through standard office applications. Security controls should focus on both application-level protections and network-based detection capabilities to identify potential exploitation attempts. Organizations must also consider the broader implications of such vulnerabilities within their overall risk management frameworks, as they can serve as initial access points for more sophisticated attacks that leverage the leaked information for further compromise.
Mitigation strategies should encompass multiple layers of defense including immediate patch deployment from Microsoft security updates, network segmentation to limit lateral movement capabilities, and enhanced monitoring of file processing activities. Organizations should implement strict file validation policies that prevent automatic execution of potentially malicious files, particularly those received through email or web-based sources. The implementation of application whitelisting solutions can significantly reduce the attack surface by restricting which applications can execute on endpoints. Security teams should also consider deploying sandboxing technologies that isolate spreadsheet processing in isolated environments to contain potential exploitation attempts. Regular security awareness training for users helps reduce the risk of social engineering attacks that leverage this vulnerability through crafted email attachments. From a compliance perspective, organizations must ensure their mitigation efforts align with industry standards such as iso 27001 and nist cybersecurity framework requirements for protecting against information disclosure vulnerabilities. The vulnerability also highlights the importance of maintaining up-to-date security patches across all Microsoft Office installations and implementing robust change management processes to quickly deploy security updates. Network administrators should monitor for unusual outbound connections that might indicate data exfiltration attempts, while endpoint protection solutions should be configured to detect suspicious file processing patterns associated with memory corruption exploits.