Source: secalert@redhat.com
Multiple race conditions in the (1) mount.cifs and (2) umount.cifs programs in Samba 3.6 allow local users to cause a denial of service (mounting outage) via a SIGKILL signal during a time window when the /etc/mtab~ file exists.
Local users can exploit a race condition in Samba's mount.cifs and umount.cifs utilities to cause a denial-of-service (DoS) condition, preventing the mounting of CIFS shares. This vulnerability allows attackers to disrupt network file sharing by sending a SIGKILL signal during a specific file operation, leading to a system outage.
Step 1: Trigger Mount/Unmount: A local user initiates a mount.cifs or umount.cifs operation, which involves creating a temporary file (/etc/mtab~).
Step 2: Identify Target Process: The attacker identifies the process ID (PID) of the mount.cifs or umount.cifs process.
Step 3: Timing Attack: The attacker sends a SIGKILL signal to the identified process during the short window when /etc/mtab~ exists but before the operation is complete.
Step 4: Inconsistent State: The SIGKILL signal interrupts the mount/unmount process, leaving the system in an inconsistent state, potentially corrupting the mount table.
Step 5: DoS Condition: Subsequent attempts to mount CIFS shares fail due to the corrupted state, resulting in a denial-of-service.
The vulnerability stems from a race condition within the mount.cifs and umount.cifs programs in Samba. Specifically, the programs create a temporary file (/etc/mtab~) during mount and unmount operations. A SIGKILL signal sent to the process during the brief window when this temporary file exists can interrupt the process, leaving the system in an inconsistent state. The core issue is the lack of proper synchronization and error handling when dealing with the temporary file and the main mount table (/etc/mtab). The programs do not adequately handle the interruption, leading to a DoS condition where subsequent mount attempts fail. The root cause is the reliance on the existence of the temporary file and the lack of atomic operations or proper locking mechanisms to protect against concurrent access and signal interruptions.
No specific APT groups or malware families are directly associated with this specific CVE. However, any attacker with local access could leverage this vulnerability. This CVE is not listed on the CISA KEV list.
Monitor system logs for unexpected SIGKILL signals sent to mount.cifs or umount.cifs processes.
Analyze system logs for errors related to CIFS mount failures, especially those occurring after SIGKILL signals.
Monitor file system activity for the creation and deletion of /etc/mtab~ and /etc/mtab files, looking for inconsistencies or unexpected behavior.
Use intrusion detection systems (IDS) to monitor for suspicious process behavior, such as a process sending SIGKILL to another process.
Upgrade to a patched version of Samba. Refer to the affected products section for specific version information.
Implement robust access controls to restrict local user access. This reduces the attack surface.
Regularly audit system logs for suspicious activity, including SIGKILL signals and CIFS mount failures.
Consider using file system monitoring tools to detect and alert on suspicious file operations related to /etc/mtab and /etc/mtab~.
Implement a defense-in-depth strategy, including host-based intrusion detection and prevention systems (HIDS/HIPS).