CVE-2024-56729
📋 TL;DR
This CVE describes a memory leak vulnerability in the Linux kernel's SMB client implementation. When a lease break races with opening a cached directory, the system fails to properly release a reference to a tcon (tree connection) structure, causing a memory leak. This affects Linux systems using SMB file sharing.
💻 Affected Systems
- Linux Kernel
📦 What is this software?
Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →⚠️ Risk & Real-World Impact
Worst Case
Sustained exploitation could lead to kernel memory exhaustion, causing system instability, crashes, or denial of service.
Likely Case
Gradual memory consumption over time leading to performance degradation, particularly on systems with frequent SMB operations.
If Mitigated
Minimal impact with proper monitoring and memory limits in place.
🎯 Exploit Status
Exploitation requires triggering a lease break race condition during cached directory operations.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Patches available in stable kernel branches via provided git commits
Vendor Advisory: https://git.kernel.org/stable/c/1b9ab6b648f89441c8a13cb3fd8ca83ffebc5262
Restart Required: Yes
Instructions:
1. Update Linux kernel to patched version. 2. Check distribution-specific security advisories. 3. Reboot system after kernel update.
🔧 Temporary Workarounds
Disable SMB client caching
linuxPrevents the race condition by disabling directory caching for SMB operations
echo 0 > /proc/fs/cifs/cachedOpen
Restrict SMB access
linuxLimit SMB connections to trusted sources only
iptables -A INPUT -p tcp --dport 445 -s trusted_network -j ACCEPT
iptables -A INPUT -p tcp --dport 445 -j DROP
🧯 If You Can't Patch
- Implement memory monitoring and alerting for kernel memory usage
- Restrict SMB client usage to essential operations only
🔍 How to Verify
Check if Vulnerable:
Check kernel version and compare with patched versions from kernel git commitsCheck Version:
uname -rVerify Fix Applied:
Verify kernel version includes one of the fix commits: 1b9ab6b648f89441c8a13cb3fd8ca83ffebc5262 or related patches📡 Detection & Monitoring
Log Indicators:
- Kernel oom-killer events
- Increasing kernel memory usage in /proc/meminfo
- SMB connection errors
Network Indicators:
- Unusual SMB traffic patterns
- Multiple SMB lease break requests
SIEM Query:
source="kernel" AND ("oom" OR "memory" OR "SMB")