CVE-2026-25143 is an OS command injection vulnerability classified under CWE-78, affecting the melange package building tool developed by chainguard-dev. Melange versions from 0.10.0 up to but not including 0.40.3 contain a flaw in the patch pipeline implementation located in pkg/build/pipelines/patch.yaml. This pipeline embeds user-influenced values such as series paths, patch filenames, and numeric parameters directly into shell scripts without proper quoting or validation. As a result, shell metacharacters can break out of their intended context, enabling an attacker to inject arbitrary shell commands. The vulnerability can be triggered during melange build or license-check operations if an attacker can control patch-related inputs, which is plausible in environments like pull request-driven continuous integration (CI), build-as-a-service platforms, or scenarios where melange configurations are influenced by untrusted sources. Exploitation allows execution of arbitrary commands with the privileges of the melange build process, potentially leading to full system compromise, data exfiltration, or further lateral movement. The vulnerability has a CVSS 3.1 base score of 7.8 (high severity), reflecting its significant impact on confidentiality, integrity, and availability, combined with relatively low attack complexity but requiring user interaction (triggering a build). No known exploits in the wild have been reported yet. The issue was addressed in melange version 0.40.3 by properly quoting and validating inputs to prevent shell metacharacter injection.

For European organizations, the impact of this vulnerability can be severe, particularly for those using melange in automated build pipelines that process external or untrusted inputs such as open-source contributions or third-party patches. Successful exploitation can lead to arbitrary code execution on build hosts, compromising the integrity of software supply chains and potentially injecting malicious code into distributed packages. This threatens confidentiality by exposing sensitive build environment data, integrity by allowing tampering with build outputs, and availability by enabling denial-of-service or destructive commands. Organizations in sectors with stringent software supply chain security requirements, such as finance, healthcare, and critical infrastructure, face heightened risks. Additionally, compromised build environments can serve as footholds for further attacks within corporate networks. The vulnerability's exploitation could undermine trust in software provenance and compliance with European cybersecurity regulations like NIS2 and GDPR if personal or sensitive data is exposed or manipulated.

The primary mitigation is to upgrade melange to version 0.40.3 or later, where the vulnerability is patched. Organizations should audit their build pipelines to identify any use of affected melange versions and ensure no legacy systems remain vulnerable. Additionally, implement strict input validation and sanitization for all patch-related inputs, especially those originating from external or untrusted sources such as pull requests or automated CI triggers. Employ the principle of least privilege by running build processes with minimal necessary permissions to limit the impact of potential exploitation. Incorporate runtime monitoring and anomaly detection on build hosts to detect suspicious command executions or unusual process behavior. Where feasible, isolate build environments using containerization or sandboxing to contain any compromise. Finally, enforce strict code review and CI pipeline security policies to prevent injection of malicious inputs into build configurations.