CVE-2006-3378 in shadow
Summary
by MITRE
passwd command in shadow in Ubuntu 5.04 through 6.06 LTS, when called with the -f, -g, or -s flag, does not check the return code of a setuid call, which might allow local users to gain root privileges if setuid fails in cases such as PAM failures or resource limits.
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Analysis
by VulDB Data Team • 07/21/2019
The vulnerability identified as CVE-2006-3378 represents a critical privilege escalation flaw within the shadow package implementation on Ubuntu systems running versions 5.04 through 6.06 LTS. This issue specifically affects the passwd command when executed with the -f, -g, or -s flags, creating a dangerous condition where the system fails to properly validate the success of setuid operations. The underlying technical flaw stems from improper error handling mechanisms within the command execution flow, where the return code of setuid calls is not adequately checked, potentially allowing malicious local users to exploit this weakness for unauthorized root access.
The operational impact of this vulnerability is significant as it directly undermines the fundamental security model of Unix-like systems where privilege separation is essential for system integrity. When the passwd command is invoked with these specific flags, the system should ensure that the setuid transition to root privileges occurs successfully before proceeding with any operations. However, the absence of proper return code validation means that if the setuid call fails due to various conditions such as PAM authentication failures, resource limit constraints, or other system-level restrictions, the command continues execution without proper privilege elevation. This creates a scenario where local attackers can manipulate the system into executing commands with elevated privileges even when the normal authentication mechanisms should prevent such access.
This vulnerability aligns with CWE-252, which addresses "Unchecked Return Value" in security contexts, specifically when the return value of a privilege elevation function is not properly validated. The issue also relates to the broader category of privilege escalation techniques documented in MITRE ATT&CK framework under T1068, "Exploitation for Privilege Escalation." The flaw demonstrates how seemingly minor implementation errors in system utilities can create substantial security holes that bypass critical access controls. The vulnerability's exploitation potential is particularly concerning because it affects the core user management functionality of the system, making it a prime target for local attackers seeking to gain administrative control.
The root cause of this issue lies in the improper error handling within the shadow package's passwd command implementation. When the setuid system call fails, the application should either abort execution or handle the failure gracefully, but instead it continues processing with potentially reduced privileges or in an inconsistent state. This behavior creates an attack surface where resource constraints or authentication failures can be leveraged to achieve unintended privilege escalation. The vulnerability is particularly dangerous because it operates silently, without generating obvious error messages that would alert administrators to the compromise, making detection difficult and increasing the window of opportunity for exploitation.
Mitigation strategies for CVE-2006-3378 should focus on immediate system updates and patch deployment to address the specific implementation flaw in the shadow package. System administrators should prioritize upgrading to patched versions of Ubuntu 5.04 through 6.06 LTS, ensuring that the updated shadow package properly validates setuid return codes before proceeding with privilege escalation operations. Additional defensive measures include implementing proper system monitoring to detect unusual passwd command usage patterns and ensuring that system resource limits are properly configured to prevent the conditions that might trigger the vulnerable code path. The vulnerability also underscores the importance of thorough security auditing of core system utilities and proper implementation of error handling mechanisms in privilege elevation code paths, as outlined in security standards such as those recommended by the Open Web Application Security Project and NIST guidelines for secure coding practices.