CVE-2019-3827 in gvfs
Summary
by MITRE
An incorrect permission check in the admin backend in gvfs before version 1.39.4 was found that allows reading and modify arbitrary files by privileged users without asking for password when no authentication agent is running. This vulnerability can be exploited by malicious programs running under privileges of users belonging to the wheel group to further escalate its privileges by modifying system files without user's knowledge. Successful exploitation requires uncommon system configuration.
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Analysis
by VulDB Data Team • 08/07/2023
The vulnerability identified as CVE-2019-3827 represents a critical authorization flaw within the gvfs (GNOME Virtual File System) component that serves as a core file system abstraction layer in many Linux desktop environments. This issue specifically affects the admin backend functionality where proper permission validation mechanisms have been bypassed, creating a significant security risk for systems utilizing gvfs versions prior to 1.39.4. The flaw manifests when no authentication agent is actively running within the system, allowing unauthorized access to sensitive file operations that should normally require explicit user authentication.
The technical implementation of this vulnerability stems from an inadequate permission verification process in the gvfs admin backend subsystem. When privileged users belonging to the wheel group execute malicious programs, they can exploit this flaw to read and modify arbitrary system files without prompting for password authentication. This represents a fundamental breakdown in the principle of least privilege and demonstrates a clear violation of access control mechanisms that should prevent unauthorized modifications to critical system resources. The vulnerability operates at the system level where authentication contexts are improperly validated, allowing for privilege escalation scenarios that bypass normal security boundaries.
From an operational impact perspective, this vulnerability creates a severe risk for systems where users have elevated privileges but are not actively using authentication agents. The exploitation requires a specific system configuration where no authentication agent is running, making it less common but still potentially dangerous when present. Attackers can leverage this flaw to modify system files without user knowledge, effectively enabling silent privilege escalation attacks. The implications extend beyond simple file access, as the ability to modify system files opens doors to broader system compromise, potentially allowing attackers to install backdoors, modify security configurations, or corrupt critical system components. This vulnerability directly relates to CWE-284 which addresses improper access control issues in software systems.
The attack vector for this vulnerability requires that malicious programs run with the privileges of users belonging to the wheel group, which typically represents administrative users with elevated system access rights. This configuration is common in many Linux distributions where wheel group members have unrestricted access to system resources. The lack of authentication agent presence creates an environment where the normal authentication flow is bypassed, allowing the flawed permission checking logic to be exploited. This scenario represents a specific edge case that attackers must carefully craft their exploitation strategy around, making the vulnerability less frequently encountered but no less dangerous when successfully exploited.
Mitigation strategies for CVE-2019-3827 primarily focus on updating to gvfs version 1.39.4 or later where the permission checking logic has been properly implemented. System administrators should ensure that all systems utilizing gvfs are updated to patched versions, particularly those running in environments where wheel group users have elevated privileges. Additionally, organizations should implement monitoring for unauthorized file modifications and maintain proper authentication agent configurations to prevent exploitation of this vulnerability. The ATT&CK framework categorizes this vulnerability under privilege escalation techniques where adversaries leverage system configuration weaknesses to gain elevated access rights, making it particularly relevant for security teams implementing defensive measures against such attack patterns.