CVE-1999-0812 in Samba
Summary
by MITRE
Race condition in Samba smbmnt allows local users to mount file systems in arbitrary locations.
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Analysis
by VulDB Data Team • 05/27/2018
The vulnerability identified as CVE-1999-0812 represents a critical race condition flaw within the Samba smbmnt utility that enables local users to manipulate file system mounting operations in unauthorized locations. This issue stems from the improper handling of temporary file creation and directory permissions during the mounting process, creating a window of opportunity for malicious exploitation. The race condition occurs when the system fails to properly validate or secure the temporary directories used during the mounting procedure, allowing attackers to interfere with the process before it completes successfully.
The technical implementation of this vulnerability involves the manipulation of file system mount operations through the smbmnt component of Samba software. When a user initiates a mount operation, the system creates temporary files and directories that are subsequently used in the mounting process. Due to insufficient synchronization mechanisms and inadequate permission checks, an attacker can create malicious symbolic links or files in the temporary directories before the legitimate mount operation completes. This allows the attacker to redirect the mount operation to arbitrary locations on the file system, potentially gaining access to restricted directories or even escalating privileges to root level access.
The operational impact of this vulnerability extends beyond simple unauthorized file system access, as it can be leveraged for privilege escalation and persistent system compromise. Local users who can execute the smbmnt utility can exploit this race condition to mount file systems in locations where they would normally not have access, potentially enabling them to read or write to sensitive system directories. This vulnerability directly relates to CWE-367 which identifies the weakness of time-of-check to time-of-use race conditions, and aligns with ATT&CK technique T1068 which covers local privilege escalation through system binary manipulation. The vulnerability is particularly dangerous because it can be exploited by users with minimal privileges to gain elevated access to the system, making it a significant concern for system administrators.
Mitigation strategies for CVE-1999-0812 should focus on implementing proper synchronization mechanisms and enhancing permission controls during the mount operation process. System administrators should ensure that all temporary directories used by smbmnt are properly secured with restrictive permissions and that the utility is run with minimal required privileges. The recommended approach includes implementing atomic file creation operations, using secure temporary directory handling, and ensuring that all mount operations validate the integrity of temporary files before proceeding. Additionally, upgrading to patched versions of Samba software that address this specific race condition is essential, as the vulnerability has been recognized and corrected in subsequent releases. Organizations should also implement monitoring for unauthorized mount operations and establish proper access controls to prevent local users from executing the smbmnt utility with elevated privileges.