CVE-2023-1192: Linux Kernel Use-After-Free Vulnerability

CVE-2023-1192 Overview

A use-after-free vulnerability was discovered in the Linux Kernel's CIFS (Common Internet File System) implementation, specifically within the smb2_is_status_io_timeout() function. This memory corruption flaw occurs when CIFS transfers response data to a system call while local variables still reference the memory region. If the system call frees this memory before CIFS completes its operations, the kernel will attempt to access deallocated memory, resulting in a denial of service condition.

Critical Impact

This vulnerability allows authenticated remote attackers to cause denial of service conditions on affected Linux systems by triggering use-after-free conditions in the CIFS subsystem, potentially causing system crashes or instability.

Affected Products

• Linux Kernel (all vulnerable versions)
• Red Hat Enterprise Linux 8.0
• Red Hat Enterprise Linux 9.0

Discovery Timeline

• 2023-11-01 - CVE-2023-1192 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-1192

Vulnerability Analysis

The vulnerability resides in the CIFS client implementation within the Linux Kernel, specifically in the SMB2 protocol handling code. The use-after-free condition (CWE-416) emerges from a race condition between the CIFS subsystem and user-space system calls when processing SMB2 response data.

When the CIFS client receives response data from a remote SMB server, it transfers this data to the requesting system call. During this handoff, local variables within smb2_is_status_io_timeout() maintain pointers to the memory region containing the response data. The vulnerability occurs when the system call completes and frees this memory before the CIFS code finishes referencing it, leaving dangling pointers that the kernel subsequently dereferences.

This vulnerability can be exploited over the network by an authenticated user with low privileges. While the attack complexity is low, successful exploitation leads to high availability impact, causing denial of service through kernel crashes or system instability. The vulnerability does not impact confidentiality or integrity.

Root Cause

The root cause is improper memory lifecycle management in the CIFS SMB2 implementation. The code fails to implement proper synchronization or reference counting mechanisms to ensure that memory regions are not freed while still being accessed by kernel functions. This creates a time-of-check-time-of-use (TOCTOU) scenario where the memory state changes between when CIFS validates it and when CIFS uses it.

Attack Vector

The attack vector is network-based, requiring an authenticated attacker with low privileges. The exploitation scenario involves:

1. An attacker establishes an authenticated CIFS/SMB connection to a target Linux system
2. The attacker sends specifically crafted SMB2 requests designed to trigger the race condition
3. By timing the requests appropriately, the attacker causes the system call to free memory while CIFS still holds references
4. The subsequent use-after-free triggers kernel memory corruption, leading to denial of service

The vulnerability mechanism involves a race condition between CIFS response processing and system call memory management. When SMB2 response data is transferred to a system call, the CIFS subsystem maintains local variable pointers to this memory. If the system call deallocates this memory before CIFS completes its access operations, a use-after-free condition occurs. For detailed technical analysis, refer to the Linux Kernel Commit d527f51 and the Red Hat Bug Report #2154178.

Detection Methods for CVE-2023-1192

Indicators of Compromise

• Unexpected kernel panics or system crashes related to CIFS operations
• Kernel oops messages referencing smb2_is_status_io_timeout() or related CIFS functions
• Abnormal SMB2 traffic patterns from authenticated users
• System instability during CIFS mount operations or file transfers

Detection Strategies

• Monitor kernel logs for use-after-free errors or memory corruption warnings in the CIFS subsystem
• Deploy kernel-level monitoring tools to track CIFS function calls and memory operations
• Implement network-based detection for anomalous SMB2 request patterns that may indicate exploitation attempts
• Use SentinelOne Singularity Platform for real-time kernel-level threat detection and behavioral analysis

Monitoring Recommendations

• Enable kernel debugging and crash dump analysis to capture exploitation attempts
• Configure CIFS-specific logging to track mount operations and SMB2 protocol activity
• Implement system stability monitoring to detect denial of service conditions
• Review authentication logs for suspicious CIFS connection attempts from unexpected sources

How to Mitigate CVE-2023-1192

Immediate Actions Required

• Update the Linux Kernel to a patched version that includes commit d527f51331cace562393a8038d870b3e9916686f
• Apply vendor-specific security patches from Red Hat for Enterprise Linux 8.0 and 9.0
• Review and restrict CIFS mount permissions to limit exposure to authenticated attackers
• Consider temporarily disabling CIFS mounts on critical systems until patches are applied

Patch Information

The vulnerability has been addressed in the Linux Kernel through commit d527f51331cace562393a8038d870b3e9916686f. This fix implements proper memory synchronization to prevent the use-after-free condition. Red Hat has also released security advisories for Enterprise Linux 8.0 and 9.0. Administrators should consult the Red Hat CVE-2023-1192 Advisory for distribution-specific patch information.

Workarounds

• Restrict network access to CIFS services using firewall rules to limit potential attackers
• Implement strict authentication policies to minimize the number of users who can establish CIFS connections
• Monitor systems for signs of exploitation and be prepared to isolate affected hosts
• Consider using alternative file sharing protocols where CIFS functionality is not critical

# Configuration example - Restrict CIFS access via firewall
# Block external SMB/CIFS access (ports 445, 139)
iptables -A INPUT -p tcp --dport 445 -s ! 10.0.0.0/8 -j DROP
iptables -A INPUT -p tcp --dport 139 -s ! 10.0.0.0/8 -j DROP

# Verify kernel version after patching
uname -r

# Check if CIFS module is loaded
lsmod | grep cifs