CVE-2018-12615 in Passenger
Summary
by MITRE
An issue was discovered in switchGroup() in agent/ExecHelper/ExecHelperMain.cpp in Phusion Passenger before 5.3.2. The set of groups (gidset) is not set correctly, leaving it up to randomness (i.e., uninitialized memory) which supplementary groups are actually being set while lowering privileges.
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Analysis
by VulDB Data Team • 03/28/2023
The vulnerability identified as CVE-2018-12615 resides within the Phusion Passenger application server software, specifically in the agent/ExecHelper/ExecHelperMain.cpp file at the switchGroup() function. This represents a critical privilege escalation flaw that affects versions prior to 5.3.2, where the software fails to properly initialize the group identifier set during privilege reduction operations. The root cause stems from improper handling of supplementary group memberships when transitioning from elevated privileges to reduced privilege levels, creating a security boundary violation that can be exploited by malicious actors.
The technical flaw manifests as uninitialized memory being utilized to determine which supplementary groups are actually applied during privilege lowering operations. When the switchGroup() function executes, it should properly establish the complete set of group identifiers that the process should belong to after dropping privileges. However, due to the absence of proper initialization, the system relies on whatever values happen to reside in uninitialized memory locations, creating unpredictable behavior that can result in unintended group memberships being retained. This vulnerability falls under the category of improper initialization as classified by CWE-456, specifically addressing the failure to initialize a critical data structure that controls access permissions.
The operational impact of this vulnerability is significant as it allows attackers to potentially maintain access to resources that should be restricted to specific group memberships. When a process drops privileges, it should transition to a well-defined set of groups that align with the reduced privilege level. However, the uninitialized memory behavior can cause processes to retain group memberships that grant access to sensitive resources or capabilities that should not be available to the reduced privilege context. This creates a potential pathway for privilege escalation attacks, where an attacker could leverage this flaw to gain access to additional system resources or perform actions that would normally be restricted by proper group membership controls. The vulnerability directly relates to the ATT&CK technique T1068, which involves exploiting weaknesses in privilege management and access controls.
Mitigation strategies for CVE-2018-12615 require immediate patching of affected Phusion Passenger installations to version 5.3.2 or later, which contains the proper initialization of the group identifier set. Organizations should also implement comprehensive monitoring for unauthorized privilege changes and group membership modifications in their application server environments. Additional defensive measures include reviewing and hardening the privilege management code within the application server, implementing proper access controls for sensitive resources, and conducting thorough security assessments of all application server configurations. System administrators should also consider implementing privilege separation techniques and ensuring that all processes operate with the minimum necessary group memberships to reduce the potential impact of such vulnerabilities. The fix addresses the core issue by ensuring that group identifier sets are properly initialized before being used in privilege reduction operations, thereby preventing the reliance on uninitialized memory values that could introduce security inconsistencies.