CVE-2002-0231 in mIRC
Summary
by MITRE
Buffer overflow in mIRC 5.91 and earlier allows a remote server to execute arbitrary code on the client via a long nickname.
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Analysis
by VulDB Data Team • 06/26/2025
The vulnerability identified as CVE-2002-0231 represents a critical buffer overflow flaw within mIRC version 5.91 and earlier installations. This security weakness specifically affects the client-side application's handling of nickname data during IRC (Internet Relay Chat) communications. The flaw occurs when mIRC processes incoming nickname data from remote servers, failing to properly validate or limit the length of nickname strings. This insufficient input validation creates an exploitable condition where malicious actors can craft specially formatted nickname data that exceeds the allocated buffer space, leading to memory corruption and potential code execution.
The technical implementation of this vulnerability falls under the Common Weakness Enumeration category CWE-121, which classifies buffer overflow conditions where insufficient boundary checking allows attackers to overwrite adjacent memory locations. In the context of mIRC, when a remote server sends a nickname containing excessive characters, the application's internal buffer handling mechanism cannot accommodate the overflow, causing the program to write data beyond its allocated memory boundaries. This memory corruption can overwrite critical program structures including return addresses, function pointers, or other executable code segments, enabling remote attackers to inject and execute arbitrary code on the victim's machine with the privileges of the mIRC process.
The operational impact of this vulnerability extends beyond simple denial of service or data corruption scenarios. Attackers leveraging this flaw can potentially gain complete control over affected systems, as demonstrated by the ability to execute arbitrary code remotely. The vulnerability affects any system running mIRC 5.91 or earlier versions, making it particularly dangerous given the widespread adoption of mIRC during that period. Since IRC servers often communicate with clients using unencrypted connections, the attack vector requires minimal network access and can be executed by any remote server that has established a connection to the vulnerable client. The attack typically occurs during normal IRC operations when the client receives a nickname from another user or server, making it difficult for users to detect or prevent such attacks.
Mitigation strategies for CVE-2002-0231 primarily focus on immediate software updates and operational security measures. The most effective solution involves upgrading to mIRC version 6.0 or later, where buffer overflow protections have been implemented and input validation mechanisms have been strengthened. Organizations should also implement network segmentation and access controls to limit exposure of vulnerable systems to untrusted IRC servers. Additionally, system administrators can deploy network monitoring solutions to detect unusual nickname data patterns that might indicate exploitation attempts. From a defensive perspective, this vulnerability aligns with ATT&CK technique T1059.007 for command and script interpreter execution, as successful exploitation would allow attackers to execute commands on compromised systems. The vulnerability also demonstrates characteristics of T1133 for external remote services, since attackers can leverage the IRC protocol to deliver malicious payloads without requiring physical access to target systems. Security practitioners should also consider implementing application whitelisting policies that restrict execution of untrusted IRC clients or applications that handle user-provided data without proper input sanitization.