CVE-2021-4034 in SD-WAN Edge
Summary
by MITRE • 01/28/2022
A local privilege escalation vulnerability was found on polkit's pkexec utility. The pkexec application is a setuid tool designed to allow unprivileged users to run commands as privileged users according predefined policies. The current version of pkexec doesn't handle the calling parameters count correctly and ends trying to execute environment variables as commands. An attacker can leverage this by crafting environment variables in such a way it'll induce pkexec to execute arbitrary code. When successfully executed the attack can cause a local privilege escalation given unprivileged users administrative rights on the target machine.
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Analysis
by VulDB Data Team • 05/21/2025
The CVE-2021-4034 vulnerability represents a critical local privilege escalation flaw in the polkit framework's pkexec utility, which operates under CWE-20 Improper Input Validation and falls within the ATT&CK technique T1068 Valid Accounts for privilege escalation. This vulnerability affects systems running versions of polkit prior to 0.105, where the pkexec utility fails to properly validate command-line arguments during execution. The flaw stems from improper handling of argument counts in the command-line parsing mechanism, creating a scenario where environment variables can be inadvertently interpreted as executable commands.
The technical exploitation of this vulnerability occurs through a specific buffer overflow condition in the argument parsing logic. When pkexec is invoked with crafted environment variables, particularly those containing shell metacharacters or command sequences, the utility's argument processing routine fails to properly terminate or validate input parameters. This misconfiguration allows attackers to inject malicious code that gets executed with elevated privileges, bypassing the intended access controls of the setuid mechanism. The vulnerability specifically manifests when the program attempts to process environment variables as if they were command arguments, creating a path for arbitrary code execution.
The operational impact of CVE-2021-4034 is severe and far-reaching, as it enables unprivileged users to gain administrative access to target systems without requiring authentication or specific credentials. This privilege escalation occurs through the exploitation of the setuid bit on pkexec, which is designed to allow authorized users to execute commands with elevated privileges according to predefined policies. Attackers can leverage this vulnerability to execute malicious payloads, establish persistent backdoors, modify system files, or extract sensitive data from compromised systems. The vulnerability affects a wide range of Linux distributions including Ubuntu, Debian, Fedora, and CentOS, making it particularly dangerous in enterprise environments.
Mitigation strategies for CVE-2021-4034 should include immediate patching of affected polkit versions to 0.105 or later, which resolves the argument parsing vulnerability. System administrators should also implement additional security controls such as monitoring for unusual pkexec executions, restricting access to the pkexec binary through file permissions, and implementing proper environment variable sanitization in system configurations. The vulnerability highlights the importance of proper input validation and argument handling in setuid applications, emphasizing the need for comprehensive security reviews of privilege escalation mechanisms. Organizations should also consider implementing privilege separation techniques and regularly auditing setuid binaries to prevent similar vulnerabilities from being exploited in the future.