CVE-2021-3917 in coreos-installer
Summary
by MITRE • 08/24/2022
A flaw was found in the coreos-installer, where it writes the Ignition config to the target system with world-readable access permissions. This flaw allows a local attacker to have read access to potentially sensitive data. The highest threat from this vulnerability is to confidentiality.
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Analysis
by VulDB Data Team • 09/25/2022
The vulnerability identified as CVE-2021-3917 resides within the coreos-installer tool, a critical component used for installing and configuring Fedora CoreOS systems. This flaw represents a significant security oversight that directly impacts the confidentiality of system data through improper file permission handling during the installation process. The coreos-installer serves as the primary mechanism for deploying Fedora CoreOS images to target systems, making it a crucial element in the system provisioning pipeline where security controls must be rigorously enforced.
The technical flaw manifests when the coreos-installer writes Ignition configuration files to the target system with world-readable access permissions. Ignition configurations typically contain sensitive information including but not limited to user credentials, network configurations, encryption keys, and system-specific parameters that could be exploited by malicious actors. This improper permission setting violates fundamental security principles and creates an attack surface where local users can access configuration data that should remain restricted to authorized administrative personnel. The vulnerability specifically affects the file system permissions applied during the installation process, where the installer fails to properly set restrictive permissions on the generated configuration files.
The operational impact of this vulnerability extends beyond simple data exposure, as it creates a persistent threat vector that remains active throughout the system lifecycle. Local attackers with minimal privileges can exploit this flaw to extract sensitive configuration data, potentially enabling them to gain deeper insights into the target system's architecture and security posture. The confidentiality threat is particularly severe because Ignition configurations often contain embedded secrets, authentication tokens, and system parameters that could facilitate further attacks, privilege escalation, or lateral movement within the network environment. This vulnerability undermines the principle of least privilege and creates opportunities for attackers to gather intelligence that could be used in more sophisticated attacks.
Security controls for this vulnerability should focus on implementing proper file permission management during the installation process, ensuring that configuration files are created with restrictive access controls that limit read access to authorized users only. The remediation approach involves modifying the coreos-installer code to enforce appropriate umask settings and explicit permission controls when writing Ignition configuration files. Organizations should also implement regular security assessments to identify similar permission-related vulnerabilities in other system components and establish automated checks to validate file permissions during system deployment. This vulnerability aligns with CWE-732, which addresses inadequate permission management, and represents a clear violation of the principle of least privilege that is fundamental to secure system design. The threat model for this vulnerability should consider both local privilege escalation scenarios and information disclosure attacks that could be leveraged to gain additional system access or intelligence.