CVE-2026-23220
📋 TL;DR
A vulnerability in the Linux kernel's ksmbd SMB server module causes an infinite loop when processing malformed SMB2 requests with invalid signatures. This leads to denial of service through high CPU consumption and log flooding. Systems running affected Linux kernel versions with ksmbd enabled are vulnerable.
💻 Affected Systems
- Linux kernel
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Complete denial of service on affected systems due to 100% CPU consumption, potentially requiring physical reboot if kernel becomes unresponsive.
Likely Case
Degraded system performance, log flooding, and potential service disruption for SMB file sharing services.
If Mitigated
Minimal impact if ksmbd is disabled or systems are patched; normal operations continue.
🎯 Exploit Status
Exploitation requires sending specially crafted SMB2 packets with invalid signatures to trigger the error path.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel versions containing commit 5accdc5b7f28a81bbc5880ac0b8886e60c86e8c8 or later
Vendor Advisory: https://git.kernel.org/stable/c/5accdc5b7f28a81bbc5880ac0b8886e60c86e8c8
Restart Required: Yes
Instructions:
1. Update Linux kernel to patched version from your distribution. 2. Reboot system to load new kernel. 3. Verify ksmbd module loads correctly if needed.
🔧 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 traffic
linuxUse firewall rules to block SMB traffic to vulnerable systems
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 for operations
- Implement network segmentation to restrict SMB access to trusted sources only
🔍 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 is patched: uname -r and verify against distribution security advisories. Confirm ksmbd module loads without issues.📡 Detection & Monitoring
Log Indicators:
- Repeated 'bad smb2 signature' messages in kernel logs (dmesg)
- High CPU usage by kernel processes
Network Indicators:
- Multiple SMB2 connection attempts with malformed packets
- Unusual SMB traffic patterns
SIEM Query:
source="kernel" AND "bad smb2 signature" OR process_cpu_usage>90 AND process_name="ksmbd"🔗 References
- https://git.kernel.org/stable/c/010eb01ce23b34b50531448b0da391c7f05a72af
- https://git.kernel.org/stable/c/5accdc5b7f28a81bbc5880ac0b8886e60c86e8c8
- https://git.kernel.org/stable/c/71b5e7c528315ca360a1825a4ad2f8ae48c5dc16
- https://git.kernel.org/stable/c/9135e791ec2709bcf0cda0335535c74762489498
- https://git.kernel.org/stable/c/f7b1c2f5642bbd60b1beef1f3298cbac81eb232c
- https://git.kernel.org/stable/c/fb3b66bd72deb5543addaefa67963b34fb163a7b
