CVE-2025-40039
📋 TL;DR
A race condition vulnerability exists in the Linux kernel's ksmbd (SMB server) component where improper locking allows concurrent access to RPC handle lists. This could lead to data corruption, crashes, or potential privilege escalation. Systems running affected Linux kernel versions with ksmbd enabled are vulnerable.
💻 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 →⚠️ Risk & Real-World Impact
Worst Case
Kernel panic, denial of service, or potential privilege escalation leading to full system compromise.
Likely Case
System instability, crashes, or denial of service affecting SMB file sharing functionality.
If Mitigated
Minimal impact if ksmbd is disabled or proper access controls limit exposure.
🎯 Exploit Status
Exploitation requires race condition triggering and access to ksmbd service. No public exploits known at this time.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Patches available in stable kernel trees (commits: 305853cce379, 5cc679ba0f45, 69674b029002, 6b615a8fb3af, 6bd7e0e55dce)
Vendor Advisory: https://git.kernel.org/stable/c/305853cce379407090a73b38c5de5ba748893aee
Restart Required: Yes
Instructions:
1. Update to patched kernel version from your distribution vendor. 2. Reboot system to load new kernel. 3. Verify ksmbd module loads correctly.
🔧 Temporary Workarounds
Disable ksmbd module
linuxPrevent loading of vulnerable ksmbd kernel module
echo 'blacklist ksmbd' >> /etc/modprobe.d/blacklist-ksmbd.conf
rmmod ksmbd
Restrict SMB network access
linuxUse firewall rules to limit access to ksmbd service
iptables -A INPUT -p tcp --dport 445 -j DROP
iptables -A INPUT -p tcp --dport 139 -j DROP
🧯 If You Can't Patch
- Disable ksmbd service and use alternative SMB implementations
- Implement strict network segmentation and access controls for SMB services
🔍 How to Verify
Check if Vulnerable:
Check if ksmbd module is loaded: lsmod | grep ksmbdCheck Version:
uname -rVerify Fix Applied:
Check kernel version includes patch commits or verify from distribution security advisory📡 Detection & Monitoring
Log Indicators:
- Kernel panic messages
- ksmbd crash logs in dmesg or journalctl
- Unexpected SMB service restarts
Network Indicators:
- Unusual SMB protocol errors
- Failed RPC connections to ksmbd
SIEM Query:
source="kernel" AND ("panic" OR "Oops") OR source="ksmbd" AND ("error" OR "crash")🔗 References
- https://git.kernel.org/stable/c/305853cce379407090a73b38c5de5ba748893aee
- https://git.kernel.org/stable/c/5cc679ba0f4505936124cd4179ba66bb0a4bd9f3
- https://git.kernel.org/stable/c/69674b029002b1d90b655f014bdf64f404efa54d
- https://git.kernel.org/stable/c/6b615a8fb3af0baf8126cde3d4fee97d57222ffc
- https://git.kernel.org/stable/c/6bd7e0e55dcea2cf0d391bbc21c2eb069b4be3e1
