The Zen C compiler, a systems programming language compiling to GNU C/C11, contained an OS command injection vulnerability (CWE-78) identified as CVE-2026-28207. This vulnerability existed in versions prior to 0.4.2 within the main application logic (src/main.c), where the compiler constructed a shell command string to invoke the backend C compiler. The construction concatenated user-controlled input—specifically the output filename provided via the '-o' command-line argument—directly into a command string executed by the system() function. Because system() invokes a shell, any shell metacharacters embedded in the output filename were interpreted and executed, enabling arbitrary command execution. An attacker with the ability to influence the compiler's command-line arguments, such as through compromised build scripts or CI/CD pipeline configurations, could exploit this vulnerability to execute arbitrary commands with the privileges of the user running the compiler. This could lead to unauthorized code execution, modification of build artifacts, or further system compromise. The vulnerability was addressed in Zen C version 0.4.2 by eliminating system() calls and introducing an ArgList mechanism for safe internal argument handling, preventing shell interpretation of user inputs. The CVSS 3.1 base score of 6.6 reflects a local attack vector requiring user interaction but with low attack complexity and no privileges required initially. No known exploits have been reported in the wild, but the vulnerability poses a risk in development environments where Zen C is used.

The primary impact of this vulnerability is unauthorized code execution on systems where vulnerable versions of the Zen C compiler are used. Attackers who can influence compiler invocation parameters may execute arbitrary shell commands with the privileges of the user running the compiler, potentially leading to code injection, data manipulation, or lateral movement within development environments. This can compromise the integrity of software builds, introduce malicious code into compiled binaries, or disrupt availability by executing destructive commands. Since the vulnerability requires local access or control over build scripts or CI/CD configurations, the risk is highest in environments with shared build infrastructure or automated pipelines. Organizations relying on Zen C for critical software development could face supply chain risks if attackers exploit this flaw to inject malicious code during compilation. Although no exploits are currently known in the wild, the vulnerability's presence in build tools makes it a significant concern for software integrity and trustworthiness.

To mitigate this vulnerability, 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 secure argument handling. Additionally, review and harden build scripts, CI/CD pipeline configurations, and any automation that invokes the Zen C compiler to ensure that untrusted input cannot influence command-line arguments, especially the output filename parameter. Employ strict access controls and auditing on build environments to prevent unauthorized modifications to build configurations. Consider sandboxing or isolating build processes to limit the impact of potential exploitation. Implement monitoring for unusual command executions or modifications in build artifacts. Finally, educate developers and DevOps teams about the risks of command injection vulnerabilities in build tools and the importance of secure coding and configuration practices.