CVE-2021-1492 in Authentication Proxy
Summary
by MITRE • 03/25/2021
The Duo Authentication Proxy installer prior to 5.2.1 did not properly validate file installation paths. This allows an attacker with local user privileges to coerce the installer to write to arbitrary privileged directories. If successful, an attacker can manipulate files used by Duo Authentication Proxy installer, cause Denial of Service (DoS) by deleting file(s), or replace system files to potentially achieve elevation of privileges. This is only exploitable during new installations, while the installer is running, and is not exploitable once installation has finished. Versions 5.2.1 of Duo Authentication Proxy installer addresses this issue.
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Analysis
by VulDB Data Team • 04/05/2021
The vulnerability identified as CVE-2021-1492 affects the Duo Authentication Proxy installer software version 5.2.0 and earlier, representing a critical path traversal and privilege escalation flaw within the installation process. This issue stems from inadequate input validation during file installation operations, creating a dangerous condition where local attackers can manipulate the installer's behavior to write files to unauthorized system directories. The vulnerability exists specifically within the installer's path validation mechanisms, which fail to properly sanitize or verify the destinations where installation files are written, creating a window of opportunity for malicious file placement.
The technical exploitation of this vulnerability requires an attacker to possess local user privileges and occurs exclusively during the active installation phase of the Duo Authentication Proxy software. During this window, the installer process lacks proper validation checks that would normally prevent writing to protected system directories such as system32, program files, or other privileged locations. This flaw directly maps to CWE-22, which describes improper limitation of a pathname to a restricted directory, commonly known as path traversal attacks. The installer's failure to implement proper path validation creates a direct pathway for attackers to manipulate the installation process and potentially gain elevated privileges through the replacement of critical system files.
The operational impact of CVE-2021-1492 extends beyond simple privilege escalation to encompass several serious security implications including potential denial of service conditions and system compromise. An attacker who successfully exploits this vulnerability can delete critical installation files to cause denial of service, replace legitimate system files with malicious equivalents, or manipulate the installer to install backdoors or trojans. The vulnerability's exploitable nature is time-bound and limited to the installation phase, meaning once the software installation completes, the attack surface closes. However, during the installation window, the impact can be severe as the attacker gains the ability to modify system components that are typically protected from unauthorized modification, creating potential for persistent access and system compromise.
This vulnerability aligns with several techniques documented in the MITRE ATT&CK framework, particularly focusing on privilege escalation and installation process manipulation. The attack vector leverages the principle of least privilege violation by allowing local users to write to system directories, which is a common technique in lateral movement and persistence operations. The vulnerability also demonstrates characteristics of attack chains that involve initial access through local user accounts, followed by privilege escalation and system compromise. Organizations should implement immediate mitigations by upgrading to Duo Authentication Proxy version 5.2.1 or later, which addresses the path validation issues through proper input sanitization and enhanced file destination verification. Additionally, system administrators should monitor installation processes and restrict local user privileges during software deployment to minimize the attack surface for such vulnerabilities. The fix implemented in version 5.2.1 demonstrates proper secure coding practices by ensuring that all file installation paths are validated against a whitelist of acceptable directories, preventing the installer from writing to unauthorized locations and closing this specific attack vector.