CVE-2025-37899
📋 TL;DR
A use-after-free vulnerability in the Linux kernel's ksmbd SMB server allows an attacker to potentially crash the kernel or execute arbitrary code. This affects systems running vulnerable Linux kernel versions with ksmbd enabled. Attackers could exploit this to gain elevated privileges or cause denial of service.
💻 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
Kernel panic leading to system crash, or arbitrary code execution with kernel privileges resulting in complete system compromise.
Likely Case
Kernel crash causing denial of service, potentially requiring system reboot to restore functionality.
If Mitigated
No impact if ksmbd is disabled or systems are properly patched with the kernel fix.
🎯 Exploit Status
Exploitation requires SMB access and race condition timing, making it moderately complex but feasible for skilled attackers.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Linux kernel with commit 02d16046cd11a5c037b28c12ffb818c56dd3ef43 or later stable backports
Vendor Advisory: https://git.kernel.org/stable/c/02d16046cd11a5c037b28c12ffb818c56dd3ef43
Restart Required: Yes
Instructions:
1. Update Linux kernel to version containing the fix. 2. Check with your distribution for specific kernel updates. 3. Reboot system to load new kernel.
🔧 Temporary Workarounds
Disable ksmbd module
linuxPrevent loading of the vulnerable ksmbd kernel module
echo 'blacklist ksmbd' >> /etc/modprobe.d/blacklist-ksmbd.conf
rmmod ksmbd
Block SMB ports
linuxPrevent SMB connections to vulnerable 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 completely if not required
- Implement network segmentation to restrict SMB access to trusted hosts only
🔍 How to Verify
Check if Vulnerable:
Check if ksmbd module is loaded: lsmod | grep ksmbd. If loaded and kernel version is vulnerable, system is at risk.Check Version:
uname -rVerify Fix Applied:
Verify kernel version contains fix commit: grep -q '02d16046cd11a5c037b28c12ffb818c56dd3ef43' /proc/version_signature || uname -r📡 Detection & Monitoring
Log Indicators:
- Kernel panic messages in /var/log/kern.log or dmesg
- Unexpected ksmbd process crashes
- Multiple failed SMB session setup attempts
Network Indicators:
- Unusual SMB traffic patterns, especially session setup requests during logoff
SIEM Query:
source="kernel" AND ("panic" OR "Oops" OR "general protection fault") AND process="ksmbd"🔗 References
- https://git.kernel.org/stable/c/02d16046cd11a5c037b28c12ffb818c56dd3ef43
- https://git.kernel.org/stable/c/2fc9feff45d92a92cd5f96487655d5be23fb7e2b
- https://git.kernel.org/stable/c/70ad6455139e26e85f48f95d0e21f351c1909342
- https://git.kernel.org/stable/c/931dc8a3670f71c45c0b1379ea4e92dafbda1aca
- https://git.kernel.org/stable/c/d5ec1d79509b3ee01de02c236f096bc050221b7f
- https://news.ycombinator.com/item?id=44081338
- https://sean.heelan.io/2025/05/22/how-i-used-o3-to-find-cve-2025-37899-a-remote-zeroday-vulnerability-in-the-linux-kernels-smb-implementation/
