CVE-2021-42110 in Allegro
Summary
by MITRE • 12/08/2021
An issue was discovered in Allegro Windows (formerly Popsy Windows) before 3.3.4156.1. A standard user can escalate privileges to SYSTEM if the FTP module is installed, because of DLL hijacking.
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Analysis
by VulDB Data Team • 05/30/2025
The vulnerability identified as CVE-2021-42110 represents a critical privilege escalation flaw within Allegro Windows software, formerly known as Popsy Windows, affecting versions prior to 3.3.4156.1. This issue specifically targets systems where the FTP module is installed, creating a pathway for standard users to attain SYSTEM-level privileges through a well-known exploitation technique. The vulnerability stems from improper handling of dynamic link library loading mechanisms, which allows malicious code injection at critical points during software execution. This flaw directly impacts the software's security model by undermining the principle of least privilege, where user accounts should operate with minimal necessary permissions.
The technical implementation of this vulnerability involves DLL hijacking, a technique that exploits the Windows dynamic link library loading process to execute arbitrary code with elevated privileges. When the FTP module is active, the application searches for specific DLL files in predictable locations, including the current working directory, which can be manipulated by an unprivileged user. This behavior aligns with CWE-426, which describes the weakness of allowing untrusted data to influence the command line of a system call, and more specifically relates to CWE-1237, which addresses issues in the loading of dynamic link libraries. The attack vector leverages the fact that the application does not properly validate or restrict the locations from which DLLs can be loaded, creating an opportunity for attackers to place malicious DLL files in strategic locations.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it provides attackers with complete system control and access to all resources, data, and processes running under the SYSTEM account. This elevated access level enables adversaries to install persistent backdoors, modify system configurations, access sensitive information, and potentially compromise the entire network infrastructure. The vulnerability's exploitation requires minimal user interaction beyond installing the FTP module, making it particularly dangerous in environments where users may have legitimate reasons to install third-party software components. Attackers can leverage this vulnerability to establish long-term persistence within the system and conduct reconnaissance activities without detection, as the SYSTEM-level access provides complete visibility into system operations and data access patterns.
Mitigation strategies for CVE-2021-42110 should prioritize immediate software updates to version 3.3.4156.1 or later, which includes patches addressing the DLL loading vulnerabilities. Organizations should implement strict software deployment policies to prevent unauthorized installation of potentially vulnerable modules such as the FTP component. The implementation of application whitelisting and strict DLL loading policies can help prevent exploitation attempts by restricting which libraries can be loaded from arbitrary locations. Additionally, regular security audits should verify that no vulnerable versions remain in production environments, while monitoring systems should be configured to detect unusual privilege escalation activities. The mitigation approach should align with ATT&CK technique T1068, which covers privilege escalation through DLL side-loading, and T1546, which addresses registry and file system modifications used for persistence. Network segmentation and least privilege access controls can further reduce the potential impact of successful exploitation attempts.