CVE-2001-1483 in Opie
Summary
by MITRE
One-Time Passwords In Everything (a.k.a OPIE) 2.32 and 2.4 allows remote attackers to determine the existence of user accounts by printing random passphrases if the user account does not exist and static passphrases if the user account does exist.
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Analysis
by VulDB Data Team • 06/04/2018
The vulnerability identified as CVE-2001-1483 resides within the One-Time Passwords In Everything (OPIE) authentication system version 2.32 and 2.4, representing a significant security flaw that undermines user account validation mechanisms. This issue stems from the system's improper handling of authentication requests for non-existent user accounts, creating a predictable pattern that adversaries can exploit to enumerate valid user accounts within a target system. The vulnerability specifically affects the passphrase generation logic where the system behaves differently based on whether a user account exists, thereby leaking information through its response behavior.
The technical flaw manifests in the authentication protocol's response handling where OPIE generates different types of passphrases depending on account validity. When a user account does not exist, the system produces random passphrases that appear to be valid one-time passwords, while for existing accounts, it returns static passphrases that are consistent across multiple authentication attempts. This differential response creates a clear indicator that can be exploited by attackers to distinguish between valid and invalid user accounts through simple authentication requests without requiring any prior knowledge of valid credentials.
This vulnerability directly relates to CWE-200, which addresses information exposure through improper error handling, and represents a classic example of information leakage in authentication systems. The operational impact of this flaw is substantial as it enables attackers to perform user enumeration attacks against systems utilizing OPIE, effectively reducing the attack surface by identifying valid user accounts that could then be targeted through other exploitation techniques. The vulnerability is particularly dangerous in environments where account names are not publicly disclosed, as it provides a method for attackers to discover valid usernames through passive observation of system responses.
The security implications extend beyond simple account enumeration, as this flaw aligns with techniques described in the MITRE ATT&CK framework under the credential access category, specifically targeting the enumeration of valid accounts as a prerequisite for more advanced attacks. Attackers can leverage this vulnerability to build comprehensive user dictionaries that can then be used for brute force attacks, dictionary attacks, or social engineering operations. The vulnerability essentially creates a backdoor mechanism for account discovery that bypasses traditional security controls, making it particularly concerning for systems where OPIE is deployed as a secondary authentication mechanism.
Mitigation strategies for this vulnerability involve implementing consistent response behavior regardless of account existence, ensuring that authentication systems return identical responses for both valid and invalid user accounts. The most effective approach includes modifying the OPIE implementation to generate random passphrases for all authentication requests, eliminating the distinguishable pattern that enables account enumeration. Additionally, system administrators should consider implementing account lockout mechanisms, rate limiting, and monitoring for unusual authentication patterns to detect potential exploitation attempts. The vulnerability also highlights the importance of proper error handling and response consistency in authentication systems, as outlined in various security frameworks including NIST SP 800-63 for identity and access management. Organizations utilizing OPIE should upgrade to patched versions or migrate to more modern authentication mechanisms that properly handle account validation without exposing information about account existence to unauthorized parties.