CVE-2025-38501
📋 TL;DR
The Linux kernel's ksmbd SMB server component allows repeated connections from clients with the same IP address to exhaust maximum connection limits, potentially causing denial of service by preventing legitimate client connections. This affects Linux systems running ksmbd with default configurations. The vulnerability requires network access to the SMB service.
💻 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 →⚠️ Risk & Real-World Impact
Worst Case
Complete denial of SMB service to legitimate clients due to connection exhaustion from a malicious actor repeatedly connecting from a single IP address.
Likely Case
Degraded SMB service availability during connection storms or targeted attacks, affecting file sharing and network resource access.
If Mitigated
Minimal impact with proper network segmentation, connection rate limiting, or the patch applied.
🎯 Exploit Status
Exploitation requires network access to ksmbd service and ability to establish multiple connections. No authentication required.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Linux kernel with commits 6073afe64510c302b7a0683a01e32c012eff715d, 7e5d91d3e6c62a9755b36f29c35288f06c3cd86b, cb092fc3a62972a4aa47c9fe356c2c6a01cd840b, e6bb9193974059ddbb0ce7763fa3882bd60d4dc3, or f1ce9258bcbce2491f9f71f7882b6eed0b33ec65
Vendor Advisory: https://git.kernel.org/stable/c/6073afe64510c302b7a0683a01e32c012eff715d
Restart Required: Yes
Instructions:
1. Update Linux kernel to version containing the fix commits. 2. Reboot system to load new kernel. 3. Verify ksmbd module loads correctly.
🔧 Temporary Workarounds
Disable ksmbd module
linuxPrevent loading of ksmbd kernel module if not required
echo 'blacklist ksmbd' >> /etc/modprobe.d/blacklist-ksmbd.conf
rmmod ksmbd
Implement network-level connection limiting
linuxUse firewall rules to limit connections per IP to ksmbd port
iptables -A INPUT -p tcp --dport 445 -m connlimit --connlimit-above 10 --connlimit-mask 32 -j REJECT
🧯 If You Can't Patch
- Restrict network access to ksmbd service using firewall rules to trusted IPs only
- Monitor connection rates and implement alerting for abnormal connection patterns from single IPs
🔍 How to Verify
Check if Vulnerable:
Check if ksmbd module is loaded: lsmod | grep ksmbd. If loaded and kernel version predates fix commits, system is vulnerable.Check Version:
uname -rVerify Fix Applied:
Verify kernel version includes fix commits and ksmbd module loads without errors.📡 Detection & Monitoring
Log Indicators:
- High frequency of connection attempts from single IP in ksmbd logs
- Connection limit warnings or errors in system logs
Network Indicators:
- Abnormally high number of TCP connections to port 445 from single source IP
- Failed connection attempts after reaching limits
SIEM Query:
source_ip COUNT BY dest_port WHERE dest_port=445 AND protocol=TCP GROUP BY source_ip HAVING COUNT > threshold🔗 References
- https://git.kernel.org/stable/c/6073afe64510c302b7a0683a01e32c012eff715d
- https://git.kernel.org/stable/c/7e5d91d3e6c62a9755b36f29c35288f06c3cd86b
- https://git.kernel.org/stable/c/cb092fc3a62972a4aa47c9fe356c2c6a01cd840b
- https://git.kernel.org/stable/c/e6bb9193974059ddbb0ce7763fa3882bd60d4dc3
- https://git.kernel.org/stable/c/f1ce9258bcbce2491f9f71f7882b6eed0b33ec65
- https://git.kernel.org/stable/c/fa1c47af4ff641cf9197ecdb1f8240cbb30389c1
- http://www.openwall.com/lists/oss-security/2025/09/15/2
- https://github.com/keymaker-arch/KSMBDrain
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
