CVE-2021-40474: High Vulnerability in Microsoft Excel

CVE-2021-40474 is a high-severity vulnerability identified in Microsoft Excel that allows remote code execution. The CVSS score of 7.8 indicates a significant risk, especially since it requires user interaction and can lead to unauthorized access to sensitive data and system integrity breaches. Organizations utilizing affected Microsoft products must prioritize addressing this vulnerability to safeguard their systems.

The vulnerability is classified under the CVSS 3.1 standard with a vector string of CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H. With a local attack vector and low complexity, it poses a considerable threat to organizations, particularly as it requires user interaction to exploit. The potential confidentiality, integrity, and availability impacts are categorized as high, highlighting the urgency for patching.

As of now, there is no public exploit confirmed for this vulnerability, but organizations should remain vigilant. The risk to organizations includes unauthorized access to sensitive data and potential system compromises. Consequently, organizations should prioritize patching immediately.

For ongoing protection, it is crucial to stay updated on Microsoft’s security advisories and implement the necessary patches as soon as they become available. The urgency surrounding this vulnerability is underscored by its classification and potential impact, making it essential for organizations to schedule remediation swiftly.

Vulnerability Details

The official description of CVE-2021-40474 states that it is a Microsoft Excel remote code execution vulnerability. The affected products include Microsoft 365 Apps, Excel 2013 SP1, Excel 2016, Office 2019, Office Online Server, and Office Web Apps Server 2013 SP1. The vulnerability was published on October 13, 2021, and is classified with a CVSS score of 7.8 (high severity).

The attack vector is local, with low complexity and no privileges required. User interaction is a necessary component of the exploit, which adds a layer of complexity to its exploitation. The potential impacts on confidentiality, integrity, and availability are all rated as high, indicating serious risks associated with this vulnerability.

Technical Analysis

The root cause of CVE-2021-40474 stems from improper handling of objects in memory, which can lead to remote code execution if exploited. Attackers may leverage this vulnerability by tricking users into opening a malicious Excel file or template that initiates the exploit. The attack complexity is classified as low, which means that an attacker with minimal skill could potentially execute the attack successfully.

Privilege requirements are nonexistent, as no privileges are needed to exploit this vulnerability. However, user interaction is required, as the user must open the malicious file. If successfully exploited, the attacker could gain access to sensitive information and potentially control the affected system.

The potential impacts on confidentiality, integrity, and availability are all rated as high. Attackers could compromise sensitive data or disrupt critical services within an organization.

Risk & Impact Analysis

The risk to organizations includes potential unauthorized access to sensitive information and the possibility of system integrity breaches. Given the local attack vector and the requirement for user interaction, organizations must ensure that their users are aware of the risks associated with opening unsolicited or suspicious files.

This vulnerability has a significant potential blast radius, especially within organizations that utilize Microsoft Excel extensively in their daily operations. The urgency assessment based on the CVSS score highlights that organizations should address this vulnerability in their priority patch cycle due to the high severity level.

Exploitation Status

Affected Versions

The affected versions include Microsoft 365 Apps, Excel 2013 SP1, Excel 2016, Office 2019, Office Long Term Servicing Channel 2021, Office Online Server, and Office Web Apps Server 2013 SP1. Organizations should review their systems for these versions to ensure they are applying necessary patches.

Mitigation & Remediation

Organizations should apply the latest patches provided by Microsoft for the affected products. For more information on the specific patches, please refer to the Microsoft Security Response Center. Additionally, organizations can implement network controls and monitoring to detect potential exploitation attempts.

Detection Guidance

Organizations should monitor logs for unusual activity related to Excel file access, particularly focusing on files received from untrusted sources. Behavioral anomalies in user activity may indicate attempts to exploit this vulnerability. Additionally, network signatures that capture any unauthorized access attempts should be established.

AppSecure Threat Intelligence Insight

CVE-2021-40474 represents a significant concern for organizations relying on Microsoft Excel. The long-term significance of this vulnerability lies in the potential for widespread exploitation if left unaddressed. It illustrates the necessity for continuous security assessments and the importance of user training regarding safe file handling practices. Security teams should prioritize regular updates and patches as part of their overall security strategy.

For more insights on enhancing security measures, organizations can explore our comprehensive resources on penetration testing methodology and ensure they are adopting best practices for vulnerability management.

Known Exploitation Timeline

This section is not applicable as there is no known exploitation timeline for CVE-2021-40474.

EPSS Risk Context

The EPSS score for CVE-2021-40474 is 0.0534, placing it in the 90.1 percentile. This indicates a relatively low probability of exploit compared to other vulnerabilities, but organizations should remain cautious and implement appropriate security measures.