CVE-2016-4900 in Evernote
Summary
by MITRE
Untrusted search path vulnerability in Evernote for Windows versions prior to 6.3 allows remote attackers to gain privileges via a Trojan horse DLL in an unspecified directory.
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Analysis
by VulDB Data Team • 12/25/2020
The CVE-2016-4900 vulnerability represents a critical untrusted search path weakness in Evernote for Windows versions below 6.3, exposing systems to privilege escalation attacks through Trojan horse DLL manipulation. This flaw resides in the application's dynamic link library loading mechanism, where the software fails to properly validate the source and integrity of dynamically loaded components. The vulnerability stems from the application's insecure handling of library paths during runtime execution, allowing malicious actors to place specially crafted DLL files in directories that the application searches automatically.
The technical implementation of this vulnerability exploits the Windows dynamic loading process where applications search for required libraries in a specific order including the current working directory, system directories, and user-defined paths. When Evernote for Windows loads DLLs without proper validation of their origins or digital signatures, attackers can position malicious libraries in directories that the application searches before legitimate system libraries. This creates a window where the application inadvertently loads and executes attacker-controlled code with the privileges of the user running the application.
The operational impact of this vulnerability extends beyond simple code execution to encompass full system compromise when exploited by adversaries. Attackers can leverage this weakness to escalate privileges from standard user accounts to administrative levels, potentially gaining complete control over affected systems. The vulnerability is particularly dangerous because it requires no user interaction beyond launching the vulnerable Evernote application, making it an ideal candidate for automated exploitation campaigns. According to the CWE classification system, this represents a CWE-427 Uncontrolled Search Path Element vulnerability, which specifically addresses insecure library loading practices.
From an adversary perspective, this vulnerability aligns with ATT&CK technique T1068 Privilege Escalation through the use of legitimate system tools and processes to gain elevated privileges. The attack vector typically involves placing malicious DLL files in directories that Evernote searches, such as the application's installation directory or other locations in the Windows search path. The exploit chain often begins with social engineering to convince users to open malicious files or download compromised versions of Evernote, followed by automatic execution of the malicious DLL when the application loads.
Mitigation strategies for CVE-2016-4900 require immediate patching of affected Evernote versions to 6.3 or later, where the developers implemented proper DLL loading security measures. Organizations should also implement application whitelisting policies to restrict which DLLs can be loaded by the application, utilize Windows Defender Application Control or similar technologies to enforce code integrity policies, and monitor for unauthorized DLL placement in application directories. System administrators should conduct regular audits of application directories to detect suspicious files and implement security awareness training to prevent users from inadvertently executing malicious code. The vulnerability demonstrates the critical importance of secure coding practices in dynamic library loading and the necessity of following secure development lifecycle principles to prevent such exploitation vectors.