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Port 465 – SMTPS (Simple Mail Transfer Protocol Secure)

Service:

smtps

Protocol:

TCP

Port:

465

Used for:

Secure SMTP for encrypted email submission

Why It’s Open

Port 465 is used for SMTP over SSL/TLS (SMTPS), providing encrypted email submission from mail clients to mail servers. Originally designated for SMTP with SSL, it was briefly deprecated in favor of STARTTLS on port 587 but remains widely used for legacy systems and specific email security requirements.

Mail servers expose this port to allow secure email submission, particularly for legacy email clients that don’t support modern STARTTLS implementations on port 587.

Common Risks

  • SSL/TLS Vulnerabilities
    Outdated encryption protocols may be exploitable
  • Certificate Issues
    Invalid or expired certificates compromise security
  • Spam Relay
    Misconfigured servers can be used for spam distribution
  • Credential Theft
    Despite encryption, weak authentication can be exploited
  • Version Exposure
    Server banners may reveal software versions

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Enumeration & Testing

Check if it’s open:

Terminal window
nmap -sT -p 465

Test SSL/TLS:

Terminal window
openssl s_client -connect :465

Check certificate:

Terminal window
sslscan :465

What to Look For

CheckpointWhat it means
Weak SSL/TLS versionsVulnerable to known cryptographic attacks
Self-signed certificatesPotential for man-in-the-middle attacks
Open relay configurationServer may be abused for spam
Authentication not requiredMissing access controls

Mitigation

  • Modern TLS Only
    Disable older SSL/TLS versions
  • Strong Certificates
    Use valid, properly signed certificates
  • Authentication Required
    Implement strong SMTP authentication
  • Rate Limiting
    Prevent abuse through connection and sending limits
  • Regular Updates
    Keep SMTP software and security patches current
  • Real World Example

In 2021, attackers exploited misconfigured SMTPS servers using outdated TLS 1.0, allowing them to intercept encrypted email traffic and harvest credentials from multiple organizations.

TL;DR

  • Port 465 = SMTPS (Secure SMTP)
  • Legacy encrypted email submission
  • Requires current TLS versions
  • Need strong authentication

Known CVEs and Exploits

  • CVE-2021-28937 – TLS renegotiation vulnerability in mail servers
  • CVE-2020-13925 – Authentication bypass in SMTP implementations
  • CVE-2019-16508 – Buffer overflow in SMTPS handling
  • Multiple tools exist for SMTPS security testing.