CVE-2023-32246
📋 TL;DR
A race condition vulnerability in the Linux kernel's ksmbd (SMB server) module allows unintended kernel code execution during module unloading. This affects Linux systems with ksmbd enabled and could bypass Kernel Lockdown protections. The vulnerability requires local access or ability to trigger module unloading.
💻 Affected Systems
- Linux kernel with ksmbd module
📦 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 →⚠️ Risk & Real-World Impact
Worst Case
Local privilege escalation to kernel-level code execution, potentially bypassing Kernel Lockdown to execute arbitrary code with kernel privileges.
Likely Case
Kernel panic or system crash due to use-after-free during module unloading, leading to denial of service.
If Mitigated
No impact if ksmbd module is not loaded or Kernel Lockdown prevents exploitation.
🎯 Exploit Status
Requires race condition timing and ability to trigger module unloading. Local access needed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Patched in Linux kernel stable trees (commits: 5a7090ccc242, b80422474ffe, c053e389db0d, d4174505016a, eb307d09fe15)
Vendor Advisory: https://git.kernel.org/stable/c/5a7090ccc242ab009ee7769e9d7fad6644dbe9bd
Restart Required: Yes
Instructions:
1. Update Linux kernel to patched version from distribution vendor. 2. Rebuild kernel if using custom kernel with ksmbd. 3. Reboot system to load patched kernel.
🔧 Temporary Workarounds
Disable ksmbd module
allPrevent loading of vulnerable ksmbd kernel module
echo 'blacklist ksmbd' >> /etc/modprobe.d/blacklist-ksmbd.conf
rmmod ksmbd 2>/dev/null || true
Prevent module unloading
allRestrict ability to unload kernel modules
sysctl -w kernel.modules_disabled=1
🧯 If You Can't Patch
- Ensure ksmbd module is not loaded (check with 'lsmod | grep ksmbd')
- Implement strict access controls to prevent unauthorized users from unloading kernel modules
🔍 How to Verify
Check if Vulnerable:
Check if ksmbd module is loaded: 'lsmod | grep -i ksmbd'. If loaded and kernel version is unpatched, system is vulnerable.Check Version:
uname -rVerify Fix Applied:
Verify kernel version includes patched commits or check with distribution's security advisory. Confirm ksmbd module functions normally after patch.📡 Detection & Monitoring
Log Indicators:
- Kernel panic logs mentioning ksmbd or RCU callbacks
- System logs showing ksmbd module unloading during active connections
Network Indicators:
- Unexpected SMB service disruption if ksmbd is used
SIEM Query:
source="kernel" AND ("ksmbd" OR "RCU callback") AND ("panic" OR "oops" OR "BUG:")🔗 References
- https://git.kernel.org/stable/c/5a7090ccc242ab009ee7769e9d7fad6644dbe9bd
- https://git.kernel.org/stable/c/b80422474ffe44cb5e813cd6da1f1c6bc50fd9d2
- https://git.kernel.org/stable/c/c053e389db0d892e2ff5a60ec5e533b976503795
- https://git.kernel.org/stable/c/d4174505016a3b2996eb7ff1530dcabbf15d47b6
- https://git.kernel.org/stable/c/eb307d09fe15844fdaebeb8cc8c9b9e925430aa5
