CVE-2024-0646: Linux Kernel Privilege Escalation Flaw

CVE-2024-0646 Overview

CVE-2024-0646 is an out-of-bounds memory write vulnerability discovered in the Linux kernel's Transport Layer Security (kTLS) functionality. The flaw exists in how the kernel handles the splice() system call when a kTLS socket is used as the destination. A local attacker with low privileges can exploit this vulnerability to cause a system crash or potentially escalate their privileges on the affected system.

Critical Impact

Local privilege escalation vulnerability in Linux kernel kTLS implementation allows authenticated attackers to gain elevated system access or cause denial of service.

Affected Products

• Linux Kernel (multiple versions up to 6.7-rc4)
• Red Hat Enterprise Linux 8.0
• Red Hat Enterprise Linux 9.0

Discovery Timeline

• 2024-01-17 - CVE-2024-0646 published to NVD
• 2024-11-25 - Last updated in NVD database

Technical Details for CVE-2024-0646

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-bounds Write), a memory corruption issue that occurs within the kernel's TLS implementation. The kTLS (kernel TLS) subsystem is designed to offload TLS encryption and decryption operations from user space to the kernel for improved performance. When processing data through the splice() system call with a kTLS socket configured as the destination, the kernel fails to properly validate buffer boundaries, resulting in memory being written outside of allocated regions.

The vulnerability requires local access to the system, meaning an attacker must already have authenticated access or the ability to execute code on the target machine. However, the low attack complexity and lack of required user interaction make this a practical attack vector for privilege escalation scenarios.

Root Cause

The root cause lies in improper bounds checking within the kTLS splice handling code path. When the splice() function is called with a kTLS socket as the destination, the kernel does not adequately verify that the data being transferred fits within the allocated kernel buffer space. This oversight allows data to be written beyond the intended memory boundaries, corrupting adjacent kernel memory structures.

The fix, committed to the Linux kernel git repository as commit c5a595000e267, addresses this issue by implementing proper boundary validation before performing the memory write operation.

Attack Vector

The attack vector is local, requiring the attacker to have existing access to the target system. Exploitation involves:

1. Creating a kTLS socket with appropriate TLS configuration
2. Setting up a splice() operation with the kTLS socket as the destination
3. Crafting input data designed to trigger the out-of-bounds write condition
4. Leveraging the memory corruption to overwrite sensitive kernel structures

This can result in kernel panic (denial of service) or, with careful exploitation, privilege escalation to root. The vulnerability affects systems where kTLS is enabled and accessible to unprivileged users.

Detection Methods for CVE-2024-0646

Indicators of Compromise

• Unexpected system crashes or kernel panics involving TLS or networking subsystems
• Unusual splice() system calls targeting kTLS sockets from non-privileged processes
• Kernel log entries indicating memory corruption or use-after-free conditions in TLS-related code paths
• Processes unexpectedly gaining elevated privileges

Detection Strategies

• Monitor for kernel oops or panic messages referencing kTLS or splice operations in /var/log/kern.log or dmesg output
• Implement auditd rules to track splice() system calls involving socket file descriptors
• Deploy kernel exploit detection tools that can identify abnormal memory access patterns
• Use SentinelOne's behavioral AI engine to detect privilege escalation attempts following suspicious kernel interactions

Monitoring Recommendations

• Enable kernel auditing for socket-related system calls using auditctl
• Configure centralized logging to capture kernel messages across all Linux systems
• Implement real-time alerting on kernel panic events and unexpected system reboots
• Regularly review audit logs for patterns consistent with local privilege escalation attempts

How to Mitigate CVE-2024-0646

Immediate Actions Required

• Update Linux kernel to patched versions as specified in vendor advisories
• Apply Red Hat Enterprise Linux security updates (RHSA-2024:0723, RHSA-2024:0724, RHSA-2024:0725, and related advisories)
• If immediate patching is not possible, consider disabling kTLS functionality as a temporary workaround
• Restrict local access to systems to trusted users only until patches can be applied

Patch Information

The vulnerability has been addressed in the upstream Linux kernel via commit c5a595000e267. Multiple Linux distributions have released security updates:

• Red Hat Enterprise Linux: Multiple security advisories available including RHSA-2024:0723, RHSA-2024:0850, RHSA-2024:1248, and others
• Debian: LTS security update released (see Debian LTS Announcement June 2024)

For detailed tracking, refer to Red Hat Bugzilla #2253908 and the upstream kernel commit.

Workarounds

• Disable kTLS by unloading the tls kernel module: modprobe -r tls
• Blacklist the TLS module to prevent automatic loading by adding blacklist tls to /etc/modprobe.d/blacklist.conf
• Implement strict access controls to limit which users can create TLS sockets
• Use container isolation to restrict access to kernel features from untrusted workloads

# Disable kTLS module as temporary workaround
modprobe -r tls

# Prevent automatic loading of kTLS module
echo "blacklist tls" >> /etc/modprobe.d/blacklist-ktls.conf

# Verify module is not loaded
lsmod | grep tls