CVE-2000-0786 in userv
Summary
by MITRE
GNU userv 1.0.0 and earlier does not properly perform file descriptor swapping, which can corrupt the USERV_GROUPS and USERV_GIDS environmental variables and allow local users to bypass some access restrictions.
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Analysis
by VulDB Data Team • 05/27/2018
The vulnerability identified as CVE-2000-0786 affects GNU userv version 1.0.0 and earlier implementations, representing a critical security flaw in privilege escalation mechanisms. This issue stems from improper file descriptor handling during the execution of user service processes, creating a scenario where local attackers can manipulate system access controls. The flaw specifically manifests in the failure to correctly swap file descriptors, leading to corruption of critical environmental variables that govern user group memberships and access permissions within the userv framework.
The technical implementation of this vulnerability involves the manipulation of file descriptor swapping operations that occur when userv processes execute with elevated privileges. When the system attempts to switch file descriptors between different user contexts, the improper handling causes the USERV_GROUPS and USERV_GIDS environmental variables to become corrupted or overwritten with unexpected values. This corruption directly impacts the privilege separation mechanisms that userv relies upon to enforce access controls, effectively allowing local users to bypass intended security boundaries.
From an operational perspective, this vulnerability creates a significant risk for systems running affected versions of GNU userv, as it enables local users to escalate their privileges and access resources that should otherwise be restricted. The impact extends beyond simple privilege escalation, as the corruption of group membership variables can lead to unauthorized access to sensitive system resources, files, and services that are protected by group-based access controls. Attackers can exploit this flaw to gain access to data that should be restricted to specific user groups, potentially compromising system integrity and confidentiality.
The vulnerability aligns with CWE-254, which addresses weaknesses in privilege management, and demonstrates characteristics consistent with privilege escalation flaws that have been documented in various Unix-like systems. From an ATT&CK framework perspective, this issue maps to privilege escalation techniques where adversaries leverage system implementation flaws to bypass access controls and gain elevated privileges. The flaw represents a classic example of a race condition or improper resource management vulnerability that can be exploited through local user access.
Mitigation strategies for this vulnerability require immediate patching of affected GNU userv installations to versions that properly implement file descriptor swapping mechanisms. System administrators should also implement monitoring for unauthorized changes to environmental variables and establish regular security audits of user service configurations. Additional protective measures include restricting local user access to userv-enabled systems where possible, implementing proper file descriptor management practices, and ensuring that all system components undergo thorough security testing before deployment. Organizations should also consider implementing privilege separation techniques that minimize the impact of such flaws through proper sandboxing and access control mechanisms.