CVE-2025-21947
📋 TL;DR
A race condition vulnerability in the Linux kernel's ksmbd component allows type confusion between IPC messages, potentially leading to memory corruption. This affects systems using the ksmbd SMB server module. Attackers could exploit this to access unexpected memory regions.
💻 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 →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
Memory corruption leading to kernel panic, information disclosure, or potential privilege escalation if combined with other vulnerabilities.
Likely Case
System instability, crashes, or information disclosure from kernel memory.
If Mitigated
Limited impact if ksmbd is not enabled or properly isolated.
🎯 Exploit Status
Requires race condition timing and ksmbd IPC usage. Likely requires some level of access to trigger FSCTL_PIPE_TRANSCEIVE ioctl.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Patches available in Linux kernel stable trees (commits referenced in CVE)
Vendor Advisory: https://git.kernel.org/stable/c/1e8833c03a38e1d5d5df6484e3f670a2fd38fb76
Restart Required: Yes
Instructions:
1. Update Linux kernel to patched version from distribution vendor. 2. Rebuild kernel if using custom build. 3. Reboot system to load new kernel.
🔧 Temporary Workarounds
Disable ksmbd module
linuxPrevent loading of vulnerable ksmbd module
echo 'blacklist ksmbd' >> /etc/modprobe.d/blacklist-ksmbd.conf
rmmod ksmbd
Restrict SMB access
linuxUse firewall rules to limit access to SMB services
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 module if not required
- Implement network segmentation to isolate systems with ksmbd enabled
🔍 How to Verify
Check if Vulnerable:
Check if ksmbd module is loaded: lsmod | grep ksmbd. If loaded and kernel version is unpatched, system is vulnerable.Check Version:
uname -rVerify Fix Applied:
Check kernel version includes patches from git commits referenced in CVE, and verify ksmbd module version if available.📡 Detection & Monitoring
Log Indicators:
- Kernel panic logs
- ksmbd error messages in system logs
- unusual SMB connection patterns
Network Indicators:
- Unusual FSCTL_PIPE_TRANSCEIVE requests to SMB shares
- Multiple rapid IPC requests
SIEM Query:
source="kernel" AND ("panic" OR "Oops") OR source="ksmbd" AND ("error" OR "failed")🔗 References
- https://git.kernel.org/stable/c/1e8833c03a38e1d5d5df6484e3f670a2fd38fb76
- https://git.kernel.org/stable/c/3cb2b2e41541fe6f9cc55ca22d4c0bd260498aea
- https://git.kernel.org/stable/c/6321bbda4244b93802d61cfe0887883aae322f4b
- https://git.kernel.org/stable/c/76861630b29e51373e73e7b00ad0d467b6941162
- https://git.kernel.org/stable/c/e2ff19f0b7a30e03516e6eb73b948e27a55bc9d2
- https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html
