CVE-2025-38562
📋 TL;DR
A null pointer dereference vulnerability in the Linux kernel's ksmbd module could cause kernel crashes or denial of service when clients send multiple Kerberos-authenticated session setup requests. This affects systems using ksmbd (kernel SMB server) with Kerberos authentication enabled. The vulnerability has a CVSS score of 5.5 (Medium severity).
💻 Affected Systems
- Linux kernel with ksmbd module enabled
📦 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 leading to system crash and complete denial of service, requiring physical or remote console access to reboot the system.
Likely Case
Kernel crash or system instability affecting SMB file sharing services, causing temporary service disruption until system recovery.
If Mitigated
Minimal impact with proper monitoring and rapid recovery procedures in place; service interruption limited to minutes.
🎯 Exploit Status
Exploitation requires Kerberos authentication and sending specific malformed session setup requests. No public exploit code available at this time.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Patched in Linux kernel stable releases (commits: 015ef163d65496ae3ba6192c96140a22743f0353, 2a30ed6428ce83afedca1a6c5c5c4247bcf12d0e, 96a82e19434a2522525baab59c33332658bc7653, 9b493ab6f35178afd8d619800df9071992f715de, 9c2dbbc959e1fcc6f603a1a843e9cf743ba383bb)
Vendor Advisory: https://git.kernel.org/stable/c/015ef163d65496ae3ba6192c96140a22743f0353
Restart Required: Yes
Instructions:
1. Update Linux kernel to patched version from your distribution's repositories. 2. Reboot system to load new kernel. 3. Verify ksmbd module loads correctly after reboot.
🔧 Temporary Workarounds
Disable ksmbd module
LinuxUnload ksmbd kernel module if not required for your use case
sudo rmmod ksmbd
echo 'blacklist ksmbd' | sudo tee /etc/modprobe.d/ksmbd-blacklist.conf
Disable Kerberos authentication for SMB
LinuxConfigure ksmbd to use only NTLM authentication instead of Kerberos
# Edit ksmbd configuration to remove Kerberos options
# Restart ksmbd service after configuration changes
🧯 If You Can't Patch
- Monitor system logs for kernel panic or crash events related to ksmbd
- Implement network segmentation to restrict access to SMB services
🔍 How to Verify
Check if Vulnerable:
Check if ksmbd module is loaded: 'lsmod | grep ksmbd'. If loaded and using Kerberos authentication, system may be vulnerable.Check Version:
uname -rVerify Fix Applied:
Check kernel version against patched releases and verify ksmbd module loads without errors in system logs.📡 Detection & Monitoring
Log Indicators:
- Kernel panic messages
- ksmbd crash logs in /var/log/kern.log or journalctl
- SMB session setup failures with Kerberos
Network Indicators:
- Multiple SMB session setup requests from same client with Kerberos authentication
- Abnormal SMB traffic patterns
SIEM Query:
source="kernel" AND ("panic" OR "Oops") AND "ksmbd" OR source="ksmbd" AND "session setup" AND "krb5"🔗 References
- https://git.kernel.org/stable/c/015ef163d65496ae3ba6192c96140a22743f0353
- https://git.kernel.org/stable/c/2a30ed6428ce83afedca1a6c5c5c4247bcf12d0e
- https://git.kernel.org/stable/c/96a82e19434a2522525baab59c33332658bc7653
- https://git.kernel.org/stable/c/9b493ab6f35178afd8d619800df9071992f715de
- https://git.kernel.org/stable/c/9c2dbbc959e1fcc6f603a1a843e9cf743ba383bb
- https://git.kernel.org/stable/c/d79c8bebaa622ee223128be7c66d8aaeeb634a57
- https://www.zerodayinitiative.com/advisories/ZDI-25-917/
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
