CVE-2025-38244
📋 TL;DR
A deadlock vulnerability in the Linux kernel's SMB client implementation can cause system hangs when reconnecting SMB channels. This affects Linux systems using CIFS/SMB file sharing, potentially leading to denial of service. The vulnerability requires SMB/CIFS usage to be exploitable.
💻 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 →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
Complete system hang requiring hard reboot, causing extended downtime and potential data loss for SMB-dependent services.
Likely Case
Temporary service disruption affecting SMB file operations until the deadlock resolves or system is restarted.
If Mitigated
Minor performance degradation during SMB reconnection events with proper kernel patching.
🎯 Exploit Status
Exploitation requires specific timing and SMB session state conditions to trigger the deadlock. No remote code execution or privilege escalation.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel versions with commits 711741f94ac3cf9f4e3aa73aa171e76d188c0819, 7f3ead8ebc0ef65b6c89a13912b4e80218425629, c82c7041258d96e3286f6790ab700e4edd3cc9e3, or fe035dc78aa6ca8f862857d45beaf7a0e03206ca
Vendor Advisory: https://git.kernel.org/stable/c/711741f94ac3cf9f4e3aa73aa171e76d188c0819
Restart Required: Yes
Instructions:
1. Update Linux kernel to patched version from your distribution's repositories. 2. Reboot system to load new kernel. 3. Verify kernel version matches patched release.
🔧 Temporary Workarounds
Disable SMB/CIFS client
linuxPrevent use of vulnerable SMB client functionality by disabling CIFS module
modprobe -r cifs
echo 'blacklist cifs' >> /etc/modprobe.d/blacklist.conf
Use alternative file sharing
linuxReplace SMB mounts with NFS or other protocols until patched
🧯 If You Can't Patch
- Monitor SMB connections and restart cifsd processes if hangs occur
- Implement redundant SMB connections with automatic failover to minimize disruption
🔍 How to Verify
Check if Vulnerable:
Check if system uses CIFS/SMB mounts and has unpatched kernel. Run: mount | grep -E '(cifs|smb)' and uname -rCheck Version:
uname -rVerify Fix Applied:
Verify kernel version includes fix commits. Check with: grep -r '711741f94ac3cf9f4e3aa73aa171e76d188c0819' /usr/src/linux📡 Detection & Monitoring
Log Indicators:
- Kernel logs showing 'possible circular locking dependency' or 'deadlock' messages related to cifsd
- System hangs during SMB operations
- Increased cifsd process CPU usage without progress
Network Indicators:
- SMB connections timing out without normal disconnection
- Unresponsive SMB file operations
SIEM Query:
source="kernel" AND ("circular locking" OR "deadlock" OR "cifs_signal_cifsd")