CVE-2021-43255 Microsoft CVE debrief

Who should care

Organizations running affected Microsoft Office versions should prioritize patching, particularly those with users who regularly handle documents from external or untrusted sources. Security teams should assess their exposure based on Office deployment scope and user workflows involving document review and collaboration.

Technical summary

This vulnerability exists in the Microsoft Office Trust Center, a component that manages security settings and trust decisions for Office documents. An attacker could exploit this flaw to spoof trusted content, potentially bypassing security warnings that would normally alert users to potentially malicious documents. The attack requires local access and user interaction, with the attacker needing to convince a user to open a specially crafted document. Successful exploitation could result in the user trusting malicious content that would normally be blocked or flagged by Office security features. The vulnerability does not provide confidentiality or availability impacts but could enable integrity violations through trusted execution of malicious content.

Defensive priority

medium

Recommended defensive actions

• Apply the security update provided by Microsoft for affected Office installations
• Verify that Office Trust Center settings are configured appropriately for your organization's security requirements
• Consider implementing application control policies to restrict execution of untrusted Office documents
• Monitor for suspicious Office document activity that may indicate exploitation attempts
• Review and update security awareness training to address social engineering tactics that could leverage this vulnerability

Evidence notes

The vulnerability is classified as a spoofing issue in the Office Trust Center component, which is responsible for managing security and privacy settings in Microsoft Office applications. The CVSS 3.1 vector (AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N) indicates a local attack vector requiring user interaction, with high impact to integrity but no confidentiality or availability impact. The vulnerability affects 11 distinct product configurations across multiple Office versions and architectures.

Official resources