Quick Summary
IMAP Service Running Without Encryption is a security misconfiguration where the Internet Message Access Protocol (IMAP) service is accessible without enforcing SSL/TLS encryption. This allows email credentials and message content to be transmitted in cleartext, making them susceptible to interception and credential theft.
Vulnerability Classification
| Field | Value |
|---|---|
| Vulnerability Type | Cleartext Protocol Exposure |
| CWE ID | CWE-319 – Cleartext Transmission of Sensitive Information |
| CVE ID | N/A (Configuration Issue) |
| CVSS 4.0 Base Score | 8.2 (High) |
| CVSS Vector | AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L |
| OWASP Category | A05:2021 – Security Misconfiguration |
| Attack Surface | Internal / External Network |
Affected Asset / Environment
- Service: IMAP
- Default Ports: 143 (IMAP), 993 (IMAPS – Secure)
- Platforms: Exchange, Dovecot, Courier, Cyrus IMAP
- Testing Method: Black-box / Internal Assessment
- Tools Used: Nmap, Telnet, OpenSSL
Description
The assessor observed that the IMAP service is accessible on port 143 without enforcing SSL/TLS encryption. During testing, it was possible to establish an IMAP session over an unencrypted channel.
IMAP is commonly used by email clients to access and manage mailboxes. When encryption is not enforced, usernames, passwords, and email contents may be transmitted in cleartext.
Attackers positioned within the same network segment may intercept credentials and email data using packet capture techniques.
Root Cause
The issue occurs due to improper mail server configuration where encrypted IMAP (IMAPS) is not enforced.
Common root causes include:
- IMAP enabled without SSL/TLS
- STARTTLS not enforced
- Missing or invalid TLS certificate
- Legacy client compatibility requirements
- Failure to implement secure mail configuration baseline
Business Impact
Exploitation of this vulnerability may allow attackers to capture valid email credentials. Compromised email accounts may be used for data exfiltration, phishing campaigns, or business email compromise.
Interception of email communications may expose confidential information, increasing legal and compliance risks.
Unencrypted email protocols may violate industry security standards and regulatory requirements.
Technical Impact
An attacker can:
- Capture IMAP usernames and passwords
- Intercept email messages
- Replay authentication credentials
- Perform man-in-the-middle attacks
- Use compromised credentials for lateral movement
This weakens overall email infrastructure security.
Proof of Concept (PoC)
Step1: Identify IMAP Service
nmap -sV -p 143 <target-ip>
If port 143 is open and identified as IMAP, proceed to validation.
Step2: Connect via Telnet
telnet <target-ip> 143
If server responds with IMAP banner and allows commands over plaintext, exposure exists.
Step3: Attempt Authentication
Within session:
a login testuser testpassword
If credentials are accepted or transmitted without encryption, service is insecure.
Step4: Verify TLS Support
openssl s_client -connect <target-ip>:143 -starttls imap
If TLS negotiation fails or STARTTLS is not supported, encryption is not enforced.
Exploitation Prerequisites
- Network access to port 143
- IMAP service enabled
- SSL/TLS not enforced
- Ability to capture network traffic
Remediation
It is recommended that encrypted IMAP (IMAPS) be enforced.
Recommended actions:
- Disable plaintext IMAP on port 143
- Enable IMAPS on port 993
- Enforce STARTTLS where applicable
- Install valid TLS certificates
- Restrict mail services via firewall
- Update mail client configurations to use secure protocols
After implementing changes, verify that plaintext authentication is blocked.
Detection and Monitoring
- Monitor network traffic for unencrypted IMAP sessions
- Alert on authentication attempts over port 143
- Conduct periodic encryption compliance reviews
- Enforce secure email configuration policies