CVE-2020-12423 in Firefox
Summary
by MITRE
When the Windows DLL "webauthn.dll" was missing from the Operating System, and a malicious one was placed in a folder in the user's %PATH%, Firefox may have loaded the DLL, leading to arbitrary code execution. *Note: This issue only affects the Windows operating system; other operating systems are unaffected.* This vulnerability affects Firefox < 78.
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Analysis
by VulDB Data Team • 07/10/2020
The vulnerability described in CVE-2020-12423 represents a critical dynamic link library (dll) hijacking flaw within the Windows implementation of Firefox browser. This security weakness specifically targets the webauthn.dll component which is responsible for handling web authentication protocols including FIDO2 authentication. The vulnerability arises from Firefox's improper handling of missing system libraries on Windows platforms, creating an exploitable condition where attacker-controlled malicious dll files can be loaded instead of legitimate system components.
The technical mechanism behind this vulnerability involves the Windows dynamic link library loading process and the %PATH% environment variable search order. When Firefox attempts to utilize webauthn functionality on Windows systems where the legitimate webauthn.dll is absent from the system directories, the operating system searches for the required library in the user's %PATH% environment variable directories. This search behavior creates an opportunity for attackers to place a malicious webauthn.dll file in a directory that appears earlier in the %PATH% search order, causing Firefox to load and execute the attacker-controlled code instead of the legitimate system library.
This vulnerability directly maps to CWE-427 Uncontrolled Search Path and CWE-1227 Improper Neutralization of Special Elements used in a Command. The flaw demonstrates a classic path traversal attack vector where the application's failure to properly validate library loading paths allows for arbitrary code execution. The attack requires an attacker to have write access to a directory within the user's %PATH% environment variable, which is typically achievable through various means including phishing attacks, social engineering, or by compromising a user account with sufficient privileges to modify system paths.
The operational impact of this vulnerability extends beyond simple code execution, as it allows for complete system compromise through the exploitation of the browser's elevated privileges during the dll loading process. Attackers can leverage this vulnerability to escalate privileges, install persistent backdoors, or perform additional malicious activities within the compromised system. The fact that this affects Firefox versions prior to 78 means that users running older browser versions remain vulnerable, particularly in enterprise environments where browser updates may be delayed or restricted. The Windows-specific nature of this vulnerability aligns with ATT&CK technique T1059 Command and Scripting Interpreter and T1106 Native API, as it exploits native windows api loading mechanisms to achieve malicious code execution.
Mitigation strategies for this vulnerability include immediate browser updates to Firefox version 78 or later where the issue has been resolved, proper system path management to minimize writable directories in %PATH%, and implementation of application whitelisting policies to prevent unauthorized dll loading. System administrators should also conduct regular security audits to identify and remove unnecessary directories from user %PATH% variables, implement strict file system permissions, and monitor for suspicious dll loading activities. The vulnerability serves as a reminder of the importance of proper library loading security practices and the need for robust application sandboxing mechanisms to prevent privilege escalation through dynamic link library manipulation attacks.