CVE-2003-1336 in mIRC
Summary
by MITRE
Buffer overflow in mIRC before 6.11 allows remote attackers to execute arbitrary code via a long irc:// URL.
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Analysis
by VulDB Data Team • 07/14/2025
The vulnerability described in CVE-2003-1336 represents a classic buffer overflow flaw that existed in mIRC versions prior to 6.11, specifically within the handling of irc:// URLs. This type of vulnerability falls under the Common Weakness Enumeration category CWE-121, which deals with stack-based buffer overflow conditions. The flaw manifested when mIRC processed specially crafted internet relay chat URLs that contained excessive data, leading to memory corruption that could be exploited by remote attackers to execute arbitrary code on vulnerable systems. The vulnerability was particularly dangerous because it could be triggered through simple URL interactions, making it accessible to attackers who could craft malicious URLs to distribute via email, websites, or other communication channels.
The technical implementation of this buffer overflow occurred in the URL parsing mechanism of mIRC, where the application failed to properly validate the length of incoming irc:// protocol URLs before copying them into fixed-size memory buffers. When an attacker supplied a URL exceeding the allocated buffer space, the excess data would overwrite adjacent memory locations, potentially corrupting the program's execution flow. This memory corruption could allow attackers to inject and execute malicious code with the privileges of the mIRC process, which typically ran with the user's current permissions. The vulnerability was particularly concerning because mIRC was widely used for instant messaging and chat communications, making it a prime target for exploitation in social engineering campaigns.
The operational impact of this vulnerability extended beyond simple code execution, as it could lead to complete system compromise when attackers leveraged the buffer overflow to gain unauthorized access to user systems. Users who clicked on maliciously crafted URLs could find their systems infected with malware, have their chat sessions hijacked, or face complete system takeover depending on the attacker's objectives. The vulnerability was especially dangerous in corporate environments where mIRC was commonly used for internal communications, as it could provide attackers with a foothold to expand their access within network perimeters. Additionally, since mIRC was often used to connect to public chat servers, the attack surface was extensive, potentially affecting thousands of users simultaneously.
Mitigation strategies for this vulnerability primarily focused on immediate software updates to mIRC version 6.11 or later, which contained proper bounds checking for URL handling. System administrators were advised to implement strict URL filtering policies and educate users about the dangers of clicking on untrusted URLs. Network-based protections such as web application firewalls could help detect and block malicious URL patterns, while endpoint protection solutions provided additional layers of defense. The vulnerability also highlighted the importance of secure coding practices and input validation, as emphasized by the ATT&CK framework's technique T1059 for command and script injection. Organizations were encouraged to adopt comprehensive vulnerability management programs that included regular security updates, penetration testing, and security awareness training to prevent similar issues from occurring in other applications.