CVE-2009-3589 in incron
Summary
by MITRE
incron 0.5.5 does not initialize supplementary groups when running a process from a user s incrontabs, which causes the process to be run with the incrond supplementary groups and allows local users to gain privileges via an incrontab table.
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Analysis
by VulDB Data Team • 01/22/2019
The vulnerability identified as CVE-2009-3589 affects incron version 0.5.5, a file monitoring daemon that executes commands based on file system events. This flaw represents a critical privilege escalation issue within the Unix-like operating system security model, specifically targeting the supplementary group handling mechanism during process execution. The vulnerability stems from improper initialization of supplementary groups when incron processes are executed from user incrontabs, creating a security gap that allows local attackers to exploit the system's privilege structure.
The technical flaw resides in the incron daemon's execution model where it fails to properly establish the complete user context when spawning processes from incrontab entries. When a user creates an incrontab entry, the associated process should execute with the user's full set of supplementary groups to ensure proper access controls and privilege boundaries. However, incron 0.5.5 only initializes the primary group while neglecting to properly set up supplementary groups, leaving the executed process running with the supplementary groups of the incrond daemon itself rather than the intended user context. This misconfiguration creates a privilege escalation vector as the process inherits group memberships that may provide access to resources or capabilities not available to the regular user account.
This vulnerability operates under the attack pattern described in the ATT&CK framework under privilege escalation techniques, specifically targeting the "Valid Accounts" and "Process Injection" domains. The operational impact is significant as local users can leverage this weakness to execute arbitrary commands with elevated privileges, potentially gaining access to sensitive system resources, files, or network services that are protected by group-based access controls. The vulnerability is particularly dangerous because it allows attackers to bypass normal access controls without requiring authentication or complex exploitation techniques, making it an attractive target for local privilege escalation attacks.
The security implications extend beyond simple privilege escalation to encompass broader system integrity concerns. When processes execute with incorrect supplementary group memberships, they may be able to access files, directories, or system resources that should be restricted to specific group memberships. This can lead to information disclosure, system compromise, or unauthorized access to sensitive data. The vulnerability is classified as a weakness under CWE-276, which addresses improper privileges, and represents a failure in proper privilege management during process execution. Organizations running incron services are particularly vulnerable to this attack vector, as it requires no external network access and can be exploited by any local user with access to create or modify incrontab entries.
Mitigation strategies should focus on immediate patching of the incron daemon to version 0.5.6 or later, which contains the necessary fixes for proper supplementary group initialization. System administrators should also implement monitoring for unauthorized incrontab modifications and consider restricting user access to incron configuration files where possible. Additionally, the principle of least privilege should be enforced by ensuring that the incrond daemon runs with minimal required privileges and that users have appropriate access controls on their incrontab entries. The vulnerability demonstrates the critical importance of proper context initialization in security-sensitive applications and the need for comprehensive testing of privilege handling mechanisms in Unix-like systems.