CVE-2005-4741 in NetBSD
Summary
by MITRE
NetBSD 1.6, NetBSD 2.0 through 2.1, and NetBSD-current before 20051031 allows local users to gain privileges by attaching a debugger to a setuid/setgid (P_SUGID) process that performs an exec without a reset of real credentials.
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Analysis
by VulDB Data Team • 07/16/2018
This vulnerability exists in NetBSD operating systems versions 1.6 through 2.1 and the current development branch prior to October 31, 2005, representing a critical privilege escalation flaw that directly violates fundamental security principles of Unix-like systems. The vulnerability stems from a flaw in how the kernel handles credential management during process execution, specifically when a process with setuid/setgid permissions performs an exec system call without properly resetting its real credentials. This creates a persistent security boundary violation where the elevated privileges granted by the setuid/setgid bit can be maintained across process transitions, effectively allowing local attackers to retain root privileges even after executing code that should normally reset these permissions.
The technical mechanism of this vulnerability aligns with CWE-276, which describes improper privileges on resources, and specifically demonstrates how improper handling of process credentials can lead to privilege escalation. When a process with P_SUGID flag (indicating setuid/setgid status) executes a new program without proper credential reset, the kernel fails to properly revoke the elevated privileges that were originally granted through the setuid/setgid mechanism. This allows the debugger attachment to maintain access to the elevated privileges, creating a persistent backdoor for privilege escalation. The vulnerability operates at the kernel level and represents a failure in the credential management subsystem, specifically in the execve system call implementation that should enforce proper privilege boundaries.
The operational impact of this vulnerability is severe as it provides local users with a straightforward method to escalate privileges without requiring additional exploitation techniques or complex attack chains. Attackers can simply attach a debugger to a setuid/setgid process that performs an exec operation, then manipulate the process to retain its elevated privileges. This creates a persistent threat vector where any local user can potentially gain root access to the system, making it particularly dangerous in multi-user environments where local privilege escalation is a common attack vector. The vulnerability affects systems where debugging tools like gdb can attach to processes with setuid/setgid permissions, which is a standard capability in most Unix-like systems.
Mitigation strategies for this vulnerability involve both immediate system updates and operational security measures. The primary solution is to upgrade to NetBSD versions after the 20051031 release where the kernel has been patched to properly reset real credentials during exec operations. This fix implements proper credential handling that ensures setuid/setgid permissions are correctly managed across process transitions, preventing the persistence of elevated privileges. Additionally, system administrators should implement strict process monitoring and privilege separation, particularly for setuid/setgid binaries that perform exec operations. From an ATT&CK perspective, this vulnerability maps to privilege escalation techniques where adversaries leverage legitimate system tools to maintain elevated access, making it important to monitor debugger usage and process execution patterns that might indicate exploitation attempts. Organizations should also consider implementing process integrity checks and credential monitoring to detect potential exploitation attempts before they can succeed in privilege escalation.