CVE-2011-3870 in Puppet
Summary
by MITRE
Puppet 2.7.x before 2.7.5, 2.6.x before 2.6.11, and 0.25.x allows local users to modify the permissions of arbitrary files via a symlink attack on the SSH authorized_keys file.
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Analysis
by VulDB Data Team • 11/24/2021
The vulnerability identified as CVE-2011-3870 represents a significant security flaw in the Puppet configuration management system that affected multiple versions including 2.7.x before 2.7.5, 2.6.x before 2.6.11, and 0.25.x releases. This issue stems from insufficient validation of symbolic link references during the SSH authorized_keys file handling process, creating a path traversal and file permission manipulation vulnerability that local attackers can exploit to gain unauthorized access to system resources. The vulnerability specifically targets the way Puppet manages SSH authentication files, which are critical components for system security and access control.
The technical implementation of this flaw occurs when Puppet processes SSH authorized_keys files without properly validating the symbolic link targets before modifying file permissions. Attackers can create malicious symbolic links that point to arbitrary files on the system, then manipulate the Puppet configuration to traverse these links and modify permissions of sensitive files that should remain protected. This vulnerability operates under the CWE-367 principle of time-of-check to time-of-use race conditions, where the system checks file permissions at one point but the actual file modification occurs later, allowing attackers to exploit the window between these operations. The flaw is particularly dangerous because it allows local users to escalate privileges and modify permissions of files they would normally not have access to, potentially compromising the entire system.
The operational impact of CVE-2011-3870 extends beyond simple file permission manipulation as it creates a persistent backdoor for attackers who can use this vulnerability to establish long-term access to compromised systems. When Puppet is used in enterprise environments for configuration management, this vulnerability becomes particularly dangerous as it allows attackers to modify SSH keys and access credentials that control system access. The vulnerability can be exploited through the standard Puppet execution process, making it difficult to detect and trace. Attackers can leverage this flaw to modify permissions of critical system files, potentially creating new user accounts, modifying system binaries, or establishing persistent access mechanisms that persist across system reboots.
Security mitigations for this vulnerability primarily involve upgrading to patched versions of Puppet where the symbolic link validation has been implemented. Organizations should immediately apply the official patches released by Puppet Labs for versions 2.7.5, 2.6.11, and 2.5.11 respectively. Additionally, system administrators should implement monitoring for unusual file permission changes in SSH-related directories and conduct regular security audits of Puppet configurations to ensure proper symlink handling. The vulnerability demonstrates the importance of proper input validation and the principle of least privilege in system security, as the flaw could be addressed through proper file system access controls and validation mechanisms that prevent unauthorized symbolic link resolution. Network defenders should also consider implementing process monitoring for Puppet execution and file system changes in sensitive directories to detect potential exploitation attempts.