CVE-2002-0425 in mIRC
Summary
by MITRE
mIRC DCC server protocol allows remote attackers to gain sensitive information such as alternate IRC nicknames via a "100 testing" message in a DCC connection request that cannot be ignored or canceled by the user, which may leak the alternate nickname in a response message.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 09/17/2025
The vulnerability described in CVE-2002-0425 affects the mIRC DCC server protocol implementation and represents a significant information disclosure flaw that enables remote attackers to extract sensitive user data. This issue specifically targets the DCC (Direct Client-to-Client) communication mechanism within the mIRC client software, which is widely used for peer-to-peer file transfers and direct messaging between IRC users. The vulnerability exploits a design weakness in how mIRC handles DCC connection requests, particularly when processing specific message types that are not properly sanitized or validated by the client software.
The technical flaw manifests when mIRC receives a DCC connection request containing a "100 testing" message, which serves as a probe to test the connectivity and capabilities of the target client. This particular message type cannot be ignored or canceled by the user interface, forcing the client to process it automatically. When the target mIRC client receives this message, it responds with information that includes the user's alternate IRC nickname, effectively leaking this sensitive information to the remote attacker. The vulnerability is particularly concerning because it bypasses normal user controls and security mechanisms that should prevent such information disclosure during connection establishment.
The operational impact of this vulnerability extends beyond simple information disclosure, as the leaked alternate nicknames can be used for various malicious activities including social engineering attacks, impersonation attempts, and targeted harassment. Attackers can leverage this information to craft more convincing phishing messages or to identify users who may be using multiple nicknames across different IRC networks. The vulnerability affects users who are actively connected to IRC networks and have mIRC configured to accept DCC connections, making it a persistent threat for anyone using the affected software. From a cybersecurity perspective, this vulnerability aligns with CWE-200, which covers "Information Exposure," and represents a classic example of how seemingly benign protocol features can be exploited for information gathering.
Mitigation strategies for this vulnerability require both immediate client-side patches and operational security improvements. Users should update their mIRC software to versions that properly handle DCC connection requests and implement proper message filtering mechanisms. Network administrators should consider implementing firewall rules that restrict DCC traffic or configure mIRC clients to disable DCC functionality entirely when not required. The vulnerability also highlights the importance of proper input validation and message handling in client applications, as outlined in the ATT&CK framework under T1071.004 for Application Layer Protocol: DNS and T1566.001 for Credential Access: Credential Stuffing. Organizations should also implement network monitoring to detect unusual DCC traffic patterns and establish security awareness training to help users understand the risks associated with accepting DCC connections from unknown sources.
This vulnerability demonstrates the critical importance of secure coding practices in client applications, particularly when handling network protocols that involve user interaction. The flaw represents a failure in proper protocol implementation and user interface design, where the software did not adequately protect users from potentially malicious protocol messages. The issue also underscores the need for comprehensive security testing of communication protocols and the importance of considering all possible message types that could be sent during network communication. From a defensive perspective, this vulnerability reinforces the principle that user controls must be robust and that automated processes should not bypass user consent mechanisms, especially when dealing with sensitive information disclosure scenarios.