CVE-2017-11877 in Excel
Summary
by MITRE
Microsoft Excel 2007 Service Pack 3, Microsoft Excel 2010 Service Pack 2, Microsoft Excel 2013 Service Pack 1, Microsoft Excel 2013 RT Service Pack 1, Microsoft Excel 2016, Microsoft Office Compatibility Pack Service Pack 3, Microsoft Excel Viewer 2007 Service Pack 3, and Microsoft Excel 2016 for Mac allow a security feature bypass by not enforcing macro settings on an Excel document, aka "Microsoft Excel Security Feature Bypass Vulnerability".
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Analysis
by VulDB Data Team • 01/23/2021
The Microsoft Excel Security Feature Bypass Vulnerability CVE-2017-11877 represents a critical flaw in multiple versions of Microsoft Excel software that undermines fundamental security controls designed to protect users from malicious macro code execution. This vulnerability affects Excel 2007 SP3, Excel 2010 SP2, Excel 2013 SP1, Excel 2013 RT SP1, Excel 2016, Office Compatibility Pack SP3, Excel Viewer 2007 SP3, and Excel 2016 for Mac installations. The core issue lies in the improper enforcement of macro security settings within Excel documents, creating a pathway for attackers to bypass critical security mechanisms that should prevent automatic execution of potentially harmful code.
The technical flaw stems from how Excel handles macro security policies when processing document files, specifically failing to properly validate or enforce the configured macro settings that users or administrators have established. This vulnerability allows threat actors to craft malicious Excel documents that can execute code without proper user consent or security warnings, effectively circumventing the built-in safeguards that should protect against macro-based attacks. The flaw operates at the application level within Excel's document processing engine, where it fails to properly interpret or enforce the security policies that should govern macro execution behavior. This bypass mechanism specifically targets the security feature that controls whether macros are enabled or disabled based on user preferences or organizational security policies.
The operational impact of this vulnerability is severe and far-reaching, as it enables attackers to deliver malicious payloads through seemingly legitimate Excel documents that users might open without suspicion. The vulnerability can be exploited through social engineering campaigns where users are tricked into opening infected Excel files, potentially leading to complete system compromise through techniques such as remote code execution or credential theft. Attackers can leverage this vulnerability to deploy malware, establish persistent backdoors, or perform information gathering activities without the user's knowledge or consent. The security implications extend beyond individual user systems to enterprise environments where macro-enabled documents are commonly shared and used for legitimate business purposes, creating widespread potential for organizational security breaches.
Mitigation strategies for CVE-2017-11877 should prioritize immediate patch deployment through Microsoft's security updates, which address the core enforcement mechanism failure in Excel's macro security implementation. Organizations must also implement additional protective measures such as disabling macro execution by default, implementing strict file execution policies, and enhancing user awareness training to recognize potentially malicious document attachments. Network-level protections including email filtering, sandboxing of document attachments, and endpoint detection systems should be deployed to identify and block suspicious Excel files. The vulnerability aligns with CWE-119 Improper Restriction of Operations within a Limited Access Scope, and maps to ATT&CK technique T1059.005 Command and Scripting Interpreter: Visual Basic, as it enables attackers to execute malicious code through macro-enabled documents. Security teams should also consider implementing application control policies that restrict Excel's ability to execute external code, and establish monitoring procedures to detect anomalous macro behavior within the organization's network infrastructure.