CVE-2020-36772 in CageFS
Summary
by MITRE • 01/22/2024
CloudLinux CageFS 7.0.8-2 or below insufficiently restricts file paths supplied to the sendmail proxy command. This allows local users to read and write arbitrary files outside the CageFS environment in a limited way.
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Analysis
by VulDB Data Team • 05/31/2025
The vulnerability identified as CVE-2020-36772 affects CloudLinux CageFS version 7.0.8-2 and earlier, representing a critical path traversal flaw within the sendmail proxy command implementation. This issue stems from inadequate input validation and sanitization of file paths passed to the sendmail functionality, creating a dangerous privilege escalation vector for local attackers. The vulnerability exists within the CageFS sandboxing mechanism that is designed to isolate user processes and file access within defined boundaries, yet fails to properly validate file path parameters in the sendmail proxy component. The flaw allows malicious users to bypass the intended security boundaries of the CageFS environment and access files outside their designated sandboxed areas. This represents a direct violation of the principle of least privilege and sandboxing security models that are fundamental to containerized and isolated execution environments.
The technical exploitation of this vulnerability occurs through the manipulation of file path parameters within the sendmail proxy command execution flow. When CageFS processes mail-related operations through the sendmail functionality, it fails to properly sanitize or validate the input paths, allowing attackers to inject malicious path specifications that traverse directory structures beyond the intended boundaries. The vulnerability specifically targets the sendmail proxy command which acts as an intermediary between user applications and the actual mail delivery mechanisms. Attackers can leverage this flaw to read sensitive files from system directories, potentially accessing configuration files, user credentials, or other confidential data that should remain isolated within the CageFS environment. The limited nature of the file access suggests that while the attacker can traverse directories and access files outside the sandbox, they cannot execute arbitrary code or gain full system control through this vector alone.
The operational impact of CVE-2020-36772 extends beyond simple information disclosure, as it fundamentally undermines the security model of the CageFS environment and can lead to cascading effects within multi-tenant hosting environments. In shared hosting scenarios, this vulnerability enables one user to potentially access files belonging to other users or system administrators, creating serious data confidentiality breaches. The limited file access capability means that while attackers cannot directly execute malicious code, they can still gather sensitive information through file reading operations, which can then be used for further exploitation or reconnaissance. This vulnerability aligns with CWE-22 Path Traversal and CWE-73 Path Traversal, both of which are classified as high-risk flaws in software security. The attack pattern follows typical privilege escalation techniques described in the MITRE ATT&CK framework under T1068 Privilege Escalation and T1083 File and Directory Discovery, where adversaries seek to expand their access beyond initial footholds.
Organizations utilizing CloudLinux CageFS must implement immediate remediation measures to address this vulnerability, including upgrading to version 7.0.8-3 or later where the path validation has been properly implemented. System administrators should conduct comprehensive audits of all CageFS environments to identify potentially compromised systems and ensure proper access controls are in place. The mitigation strategy should include implementing additional monitoring for unusual file access patterns and establishing strict input validation mechanisms for all proxy commands. Security teams should also consider implementing network segmentation and privilege separation to limit the potential impact of such vulnerabilities, while ensuring that all system components undergo regular security assessments and vulnerability scanning. The remediation process should also include comprehensive testing to verify that the updated version properly handles all file path parameters without introducing new security weaknesses or functionality regressions.