CVE-2008-6984 in Plesk
Summary
by MITRE
Plesk 8.6.0, when short mail login names (SHORTNAMES) are enabled, allows remote attackers to bypass authentication and send spam e-mail via a message with (1) a base64-encoded username that begins with a valid shortname, or (2) a username that matches a valid password, as demonstrated using (a) SMTP and qmail, and (b) Courier IMAP and POP3.
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Analysis
by VulDB Data Team • 11/21/2018
The vulnerability identified as CVE-2008-6984 affects Plesk version 8.6.0 and represents a critical authentication bypass flaw that specifically manifests when short mail login names are enabled within the system configuration. This vulnerability exploits a fundamental weakness in the authentication mechanism that governs email access through both SMTP and IMAP/POP3 protocols, creating a pathway for unauthorized users to gain access to email accounts without proper credentials. The flaw stems from how the system processes username validation when shortnames are enabled, allowing attackers to manipulate authentication requests through crafted base64-encoded credentials or by leveraging existing valid password matches.
The technical implementation of this vulnerability involves the manipulation of authentication tokens during email protocol interactions, particularly targeting the qmail SMTP server and Courier IMAP/POP3 implementations that are commonly integrated with Plesk email services. When short mail login names are enabled, the system's authentication routine fails to properly validate the complete username string, instead accepting partial matches or encoded credentials that begin with legitimate shortname prefixes. This creates a scenario where an attacker can construct a base64-encoded username that starts with a valid shortname, effectively bypassing the authentication layer and gaining unauthorized access to email accounts. The vulnerability operates at the protocol level, exploiting the trust relationship between the email server and client authentication mechanisms.
The operational impact of this vulnerability extends beyond simple unauthorized access to encompass significant spam distribution capabilities and potential data compromise. Attackers who successfully exploit this vulnerability can send spam emails from compromised accounts, potentially using the legitimate email infrastructure to distribute malicious content or engage in phishing campaigns. The attack vector is particularly concerning because it allows remote exploitation without requiring prior access to valid credentials, making detection more difficult and increasing the attack surface for malicious actors. The vulnerability affects the core email security model of Plesk installations, potentially enabling attackers to compromise multiple email accounts simultaneously if they can identify valid shortname prefixes within the system.
This vulnerability aligns with CWE-287, which addresses improper authentication issues, and represents a classic example of how weak input validation can lead to authentication bypass scenarios. The attack pattern follows techniques described in the ATT&CK framework under privilege escalation and initial access phases, where adversaries leverage system configuration weaknesses to gain unauthorized access to email services. Organizations using Plesk with short mail login names enabled face significant risk of email-based attacks, including spam abuse, credential harvesting, and potential data exfiltration through compromised email accounts. The vulnerability demonstrates the importance of proper authentication validation and input sanitization in email server implementations, particularly when dealing with legacy authentication mechanisms that may not adequately address modern security requirements.
Mitigation strategies for CVE-2008-6984 require immediate attention through configuration changes and system updates. The primary recommendation involves disabling short mail login names within Plesk configuration when they are not essential for business operations, as this directly eliminates the attack vector. System administrators should also implement proper input validation at the email server level, ensuring that all authentication requests undergo comprehensive credential verification regardless of the username format. Additionally, organizations should consider implementing rate limiting and monitoring mechanisms to detect unusual email sending patterns that might indicate exploitation attempts. Regular security updates and patches should be applied to Plesk installations to address known vulnerabilities, while network-level controls such as email filtering and authentication protocols like SPF, DKIM, and DMARC should be strengthened to prevent abuse of compromised accounts. The vulnerability underscores the necessity of maintaining current security practices and avoiding deprecated features that may introduce exploitable weaknesses into email infrastructure deployments.