Zen C is a systems programming language compiling to GNU C/C11 code. Versions before 0.4.2 contain a command injection vulnerability (CWE-78) in the compiler's main application logic, specifically in src/main.c. The vulnerability occurs because the compiler constructs a shell command string to invoke the backend C compiler by concatenating various arguments, including a user-controlled output filename passed via the -o command-line argument. This string is executed using the system() function, which invokes a shell to parse the command. If the output filename contains shell metacharacters, these are interpreted by the shell, allowing arbitrary command execution. An attacker who can influence the compiler's command-line arguments—such as through malicious build scripts or compromised CI/CD pipeline configurations—can execute arbitrary commands with the privileges of the user running the compiler. The vulnerability does not require prior privileges but does require the ability to influence command-line arguments and some user interaction to trigger compilation. The issue was resolved in version 0.4.2 by removing system() calls and implementing an ArgList structure for safe internal argument handling, eliminating shell interpretation of user input. No known exploits are reported in the wild as of now.

This vulnerability can lead to arbitrary code execution on systems where vulnerable versions of the Zen C compiler are used, potentially compromising the confidentiality, integrity, and availability of affected systems. Since the attacker can execute commands with the privileges of the user running the compiler, this could lead to privilege escalation if the compiler is run by privileged users or automated systems with elevated rights. In environments using automated build systems or CI/CD pipelines, a compromised or malicious build script could exploit this flaw to execute arbitrary commands, potentially leading to supply chain attacks, unauthorized access, or disruption of development workflows. The impact is particularly significant in organizations relying on Zen C for system-level programming or embedded development, where the integrity of compiled code is critical. Although exploitation requires local access or the ability to influence command-line arguments, the risk is heightened in shared development environments or where build configurations are externally controlled. The medium CVSS score reflects moderate severity but the potential for serious consequences if exploited in sensitive environments.

Organizations should immediately upgrade all instances of the Zen C compiler to version 0.4.2 or later, where the vulnerability is fixed by removing unsafe system() calls and implementing safe argument handling. Until upgrades are possible, restrict access to systems running vulnerable versions to trusted users only and audit build scripts and CI/CD pipeline configurations to ensure no untrusted input can influence compiler command-line arguments. Implement strict input validation and sanitization on any user-supplied filenames or parameters passed to the compiler. Consider running compilation processes with the least privileges necessary to limit the impact of potential exploitation. Monitor build environments for unusual command executions or unexpected behavior that could indicate exploitation attempts. Additionally, review and harden the security of CI/CD pipelines to prevent injection of malicious build commands. Employ application whitelisting and endpoint detection to detect anomalous shell command executions originating from compiler processes.