CVE-2006-4364: MDaemon POP3 server heap buffer overflow via USER and APOP commands

Automated analysis

Generated by VULONE's analysis model from the NVD record, CISA KEV and EPSS data on 19 September 2026. Confidence: medium.

high priorityRemote unauthenticated heap overflow with public exploit code and very high EPSS, though the CVSS impact is limited to partial availability loss.

What it is

Alt-N MDaemon before 9.0.6 contains multiple heap-based buffer overflows in its POP3 server. Long strings containing '@' characters in the USER and APOP commands overflow heap buffers, crashing the daemon and potentially allowing code execution.

Impact

A remote unauthenticated attacker can crash the POP3 daemon, causing denial of service, and may be able to execute arbitrary code in the server process context.

Attack surface

Reachable over the network through the POP3 service; the CVSS vector AV:N/AC:L/Au:N indicates no authentication is required and no user interaction is needed.

Exploitation

Not listed in CISA KEV, but EPSS is high at 0.56653 (99th percentile) and public references are tagged Exploit, including an Exploit-DB entry, indicating exploit code is publicly available.

What to do

• Upgrade MDaemon to version 9.0.6 or later, which the vendor release notes and advisory address.
• If immediate upgrade is not possible, restrict POP3 access to trusted networks or disable the POP3 service where unused.
• Place the POP3 service behind a filtering proxy or IPS that rejects malformed USER and APOP commands containing long '@' strings.
• Monitor vendor advisories for any follow-up fixes and verify the installed MDaemon build against the fixed version.

Detection

• Inspect POP3 server logs for USER or APOP commands containing unusually long strings or embedded '@' characters.
• Monitor for repeated MDaemon POP3 daemon crashes or restarts that correlate with inbound POP3 traffic.
• Use network IDS signatures for oversized POP3 USER/APOP arguments and alert on anomalous command lengths.
• Track process crashes of the MDaemon POP3 service and correlate with source IPs for triage.

This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.