CVE-2023-32255
📋 TL;DR
A memory leak vulnerability exists in the Linux kernel's ksmbd component when handling session setup requests with unknown NTLMSSP message types. This could lead to resource exhaustion over time, potentially causing denial of service. Systems running Linux kernels with ksmbd enabled are affected.
💻 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
Sustained exploitation could exhaust kernel memory, leading to system instability, crashes, or denial of service requiring reboot.
Likely Case
Gradual memory consumption causing performance degradation over time, potentially requiring service restarts.
If Mitigated
Minimal impact with proper monitoring and resource limits in place.
🎯 Exploit Status
Requires ability to send SMB session setup requests to ksmbd service. No authentication bypass involved.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel commit 6d7cb549c2ca20e1f07593f15e936fd54b763028 and later
Vendor Advisory: https://access.redhat.com/security/cve/CVE-2023-32255
Restart Required: Yes
Instructions:
1. Update Linux kernel to version containing fix commit 2. Rebuild kernel if compiling from source 3. Reboot system to load patched kernel
🔧 Temporary Workarounds
Disable ksmbd module
linuxUnload ksmbd kernel module if not required
sudo modprobe -r ksmbd
echo 'blacklist ksmbd' | sudo tee /etc/modprobe.d/ksmbd-blacklist.conf
Restrict SMB access
linuxUse firewall rules to limit access to ksmbd service
sudo iptables -A INPUT -p tcp --dport 445 -s trusted_network -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 445 -j DROP
🧯 If You Can't Patch
- Disable ksmbd service if not required
- Implement strict network access controls to limit SMB traffic to trusted sources only
🔍 How to Verify
Check if Vulnerable:
Check if ksmbd module is loaded: lsmod | grep ksmbd. If loaded, check kernel version against patched versions.Check Version:
uname -rVerify Fix Applied:
Verify kernel version includes fix commit 6d7cb549c2ca20e1f07593f15e936fd54b763028 or later.📡 Detection & Monitoring
Log Indicators:
- Kernel OOM (Out of Memory) messages in /var/log/kern.log or dmesg
- ksmbd service crashes or restarts
Network Indicators:
- Unusual SMB session setup requests with malformed NTLMSSP messages
SIEM Query:
source="kernel" AND ("oom" OR "out of memory") AND process="ksmbd"