CVE-2021-23192
📋 TL;DR
This vulnerability in Samba's DCE/RPC implementation allows attackers to bypass signature requirements by intercepting and modifying fragmented large requests. Attackers can inject malicious data into legitimate client-server communications. All Samba servers using affected versions are vulnerable.
💻 Affected Systems
- Samba
📦 What is this software?
Samba by Samba
Samba by Samba
Samba by Samba
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise through arbitrary code execution, data theft, or service disruption by injecting malicious payloads into authenticated sessions.
Likely Case
Privilege escalation, data manipulation, or unauthorized access to Samba shares and services by bypassing authentication controls.
If Mitigated
Limited impact with proper network segmentation, intrusion detection, and minimal exposure of Samba services.
🎯 Exploit Status
Exploitation requires network access and ability to intercept/modify traffic. Proof-of-concept code exists in security advisories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Samba 4.13.17, 4.14.12, 4.15.5 or later
Vendor Advisory: https://www.samba.org/samba/security/CVE-2021-23192.html
Restart Required: Yes
Instructions:
1. Update Samba packages using your distribution's package manager. 2. For Red Hat/CentOS: 'yum update samba'. 3. For Ubuntu/Debian: 'apt update && apt upgrade samba'. 4. Restart Samba services: 'systemctl restart smb nmb' or 'service smbd restart'.
🔧 Temporary Workarounds
Disable DCE/RPC if not needed
linuxDisable DCE/RPC protocol if not required for your Samba deployment
Edit smb.conf and add: 'rpc_server:smb = no'
Restart Samba: 'systemctl restart smb nmb'
Network segmentation
linuxRestrict Samba server access to trusted networks only
Configure firewall rules: 'iptables -A INPUT -p tcp --dport 445 -s trusted_network -j ACCEPT'
iptables -A INPUT -p tcp --dport 445 -j DROP
🧯 If You Can't Patch
- Implement strict network access controls to limit Samba exposure
- Deploy intrusion detection systems to monitor for exploitation attempts
🔍 How to Verify
Check if Vulnerable:
Check Samba version: 'smbd --version' or 'rpm -q samba' or 'dpkg -l | grep samba'. If version is below 4.13.17, 4.14.12, or 4.15.5, you are vulnerable.Check Version:
smbd --versionVerify Fix Applied:
After update, verify version is 4.13.17+, 4.14.12+, or 4.15.5+ using 'smbd --version'. Test Samba functionality remains operational.📡 Detection & Monitoring
Log Indicators:
- Unusual DCE/RPC fragmentation patterns in Samba logs
- Authentication failures followed by successful access
- Large RPC requests with unusual timing
Network Indicators:
- Abnormal TCP packet fragmentation on Samba ports (445, 139)
- Man-in-the-middle activity between Samba clients and servers
SIEM Query:
source="samba_logs" AND ("DCE/RPC" OR "fragment") AND size>threshold🔗 References
- https://bugzilla.redhat.com/show_bug.cgi?id=2019666
- https://security.gentoo.org/glsa/202309-06
- https://ubuntu.com/security/CVE-2021-23192
- https://www.samba.org/samba/security/CVE-2021-23192.html
- https://bugzilla.redhat.com/show_bug.cgi?id=2019666
- https://security.gentoo.org/glsa/202309-06
- https://ubuntu.com/security/CVE-2021-23192
- https://www.samba.org/samba/security/CVE-2021-23192.html
