CVE-2007-3729 in OpenVMS
Summary
by MITRE
The default configuration of the POP server in TCP/IP Services 5.6 for HP OpenVMS 8.3 generates different responses depending on whether or not a username is valid, which allows remote attackers to enumerate valid POP usernames.
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Analysis
by VulDB Data Team • 09/05/2018
The vulnerability described in CVE-2007-3729 represents a classic information disclosure flaw in the POP3 server implementation of HP OpenVMS TCP/IP Services 5.6 version 8.3. This issue stems from the server's failure to maintain consistent response behavior regardless of whether a provided username exists within the system's user database. The flaw manifests as differential responses to authentication attempts, where valid usernames produce different server replies compared to invalid ones, creating a side-channel information leak that adversaries can exploit to determine legitimate user accounts.
The technical mechanism behind this vulnerability operates through the POP3 protocol's authentication process where the server responds with distinct error messages or timing characteristics when processing user credentials. When an attacker submits a username to the POP server, the system's default configuration causes it to return different responses based on whether that username exists in the system's user database. This behavior creates a predictable pattern that can be systematically exploited through automated tools to distinguish between valid and invalid usernames through careful analysis of server responses.
The operational impact of this vulnerability extends beyond simple user enumeration as it provides attackers with a foundational foothold for subsequent attack phases. Once valid usernames are discovered, adversaries can proceed with brute force attacks, credential stuffing, or other authentication-related exploits that leverage this information to gain unauthorized access to the system. The vulnerability particularly affects environments where the POP server serves as an entry point for email access, potentially compromising email accounts and associated system resources. This issue directly relates to CWE-200, Information Exposure, and represents a specific instance of how improper error handling can lead to information disclosure.
From an adversary perspective, this vulnerability aligns with techniques described in the MITRE ATT&CK framework under the Initial Access and Credential Access phases. The ability to enumerate valid usernames through differential response analysis constitutes a reconnaissance technique that can be automated and scaled to identify potential targets within the email infrastructure. The attack pattern typically involves sending multiple authentication requests and analyzing response variations to build a list of valid accounts, making this vulnerability particularly dangerous in environments with large user bases or when combined with other reconnaissance efforts.
The recommended mitigations for this vulnerability center on implementing consistent error handling across the POP3 server implementation. System administrators should configure the POP server to return identical responses regardless of whether a username exists, effectively eliminating the information leakage. This approach aligns with security best practices for preventing side-channel attacks and information disclosure vulnerabilities. Additionally, implementing account lockout mechanisms and rate limiting can help reduce the effectiveness of automated enumeration attempts. The fix should also include regular security assessments and configuration reviews to ensure that default settings do not expose sensitive information. Organizations should consider upgrading to newer versions of TCP/IP Services that address this issue through improved security configurations or implementing network-level controls that limit access to the POP server from untrusted networks.