CVE-2013-4136 in Passenger
Summary
by MITRE
ext/common/ServerInstanceDir.h in Phusion Passenger gem before 4.0.6 for Ruby allows local users to gain privileges or possibly change the ownership of arbitrary directories via a symlink attack on a directory with a predictable name in /tmp/.
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Analysis
by VulDB Data Team • 01/08/2022
The vulnerability identified as CVE-2013-4136 affects the Phusion Passenger gem version 4.0.5 and earlier, representing a significant local privilege escalation and directory ownership manipulation flaw. This issue resides within the ext/common/ServerInstanceDir.h file, which handles server instance directory management during the gem's operation. The vulnerability stems from improper handling of temporary directories with predictable naming conventions, specifically those located in the /tmp/ filesystem hierarchy where symbolic link attacks can be effectively executed.
The technical flaw exploits the predictable naming patterns of temporary directories created by the Phusion Passenger gem during its runtime operations. When the gem initializes server instances, it creates directories with known, predictable names within the /tmp/ filesystem. Local attackers can leverage this predictability by creating malicious symbolic links that point to arbitrary directories before the gem attempts to create its own directory structure. This symlink attack allows adversaries to manipulate the ownership and permissions of target directories, potentially enabling privilege escalation or unauthorized access to sensitive system resources.
The operational impact of this vulnerability extends beyond simple privilege escalation as it provides attackers with the capability to modify directory ownership and potentially gain elevated system privileges. Attackers can exploit this weakness to manipulate the ownership of directories that the Phusion Passenger process would normally control, potentially leading to unauthorized access to system resources, data compromise, or further exploitation of the compromised system. The vulnerability is particularly concerning because it operates at the local privilege level, meaning attackers who already have access to a system can leverage this flaw to escalate their privileges or gain unauthorized access to system resources.
This vulnerability aligns with CWE-377, which addresses the use of insecure temporary files, and demonstrates characteristics consistent with the ATT&CK technique T1068, which involves exploiting local privilege escalation vulnerabilities. The flaw represents a classic race condition vulnerability where the timing between symlink creation and directory access creates an exploitable window. Organizations using Phusion Passenger in production environments face significant risk from this vulnerability, particularly when running applications that require elevated privileges or when multiple users share the same system resources.
The recommended mitigation strategy involves upgrading to Phusion Passenger version 4.0.6 or later, which includes proper handling of temporary directory creation and eliminates the predictable naming patterns that enable the symlink attack. System administrators should also implement additional security measures such as proper permissions on /tmp/ directory, monitoring for unauthorized symbolic link creation, and ensuring that all system components are regularly updated to address known vulnerabilities. The fix implemented in version 4.0.6 addresses the root cause by introducing proper directory creation mechanisms that prevent symbolic link attacks and ensure that temporary directories are created with appropriate security controls to prevent unauthorized access or manipulation.