CVE-2021-45856
📋 TL;DR
CVE-2021-45856 is a buffer overflow vulnerability in the telnet service of Accu-Time Systems MAXIMUS 1.0 time and attendance systems. Attackers can send specially crafted packets to crash the telnet service, causing denial of service. Organizations using MAXIMUS 1.0 systems with telnet enabled are affected.
💻 Affected Systems
- Accu-Time Systems MAXIMUS
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system unavailability due to telnet service crash, potentially disrupting time tracking and payroll operations.
Likely Case
Telnet service becomes unresponsive, requiring manual restart and causing temporary service disruption.
If Mitigated
Minimal impact if telnet is disabled or network access is restricted.
🎯 Exploit Status
Proof-of-concept exploit code is publicly available on Packet Storm. Exploitation requires sending malformed telnet packets.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Not available
Vendor Advisory: Not available
Restart Required: No
Instructions:
No official patch available. Contact Accu-Time Systems for potential firmware updates or mitigation guidance.
🔧 Temporary Workarounds
Disable Telnet Service
allCompletely disable the telnet service if remote access is not required.
Consult MAXIMUS system administration guide for telnet disable procedure
Restrict Network Access
linuxUse firewall rules to restrict access to telnet port (default TCP 23) to trusted IPs only.
iptables -A INPUT -p tcp --dport 23 -s [TRUSTED_IP] -j ACCEPT
iptables -A INPUT -p tcp --dport 23 -j DROP
🧯 If You Can't Patch
- Implement strict network segmentation to isolate MAXIMUS systems from untrusted networks
- Monitor telnet service logs for crash events and implement alerting
🔍 How to Verify
Check if Vulnerable:
Check if MAXIMUS 1.0 is running with telnet service enabled on port 23. Attempt to connect via telnet to verify service availability.Check Version:
Check system firmware version through MAXIMUS web interface or console: System > About or similar menuVerify Fix Applied:
Verify telnet service is disabled or inaccessible. Test with telnet client to confirm connection refusal.📡 Detection & Monitoring
Log Indicators:
- Telnet service crash logs
- Unexpected telnet connection attempts
- System restart events following telnet activity
Network Indicators:
- Multiple connection attempts to TCP port 23
- Malformed telnet packets detected by IDS/IPS
SIEM Query:
source="MAXIMUS" AND (event="telnet_crash" OR event="service_stop")