CVE-2000-0190 in Instant Messenger
Summary
by MITRE
AOL Instant Messenger (AIM) client allows remote attackers to cause a denial of service via a message with a malformed ASCII value.
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Analysis
by VulDB Data Team • 04/21/2026
The vulnerability identified as CVE-2000-0190 represents a classic denial of service flaw within the AOL Instant Messenger client implementation. This vulnerability specifically targets the message parsing mechanism of the AIM client, where malformed ASCII values in incoming messages can trigger unexpected behavior leading to system instability. The flaw exists in the client-side processing logic that fails to properly validate or sanitize incoming message data before attempting to display or process it. This type of vulnerability falls under the broader category of input validation failures that have been consistently documented in security literature and classified under CWE-20, which addresses "Improper Input Validation" as a fundamental weakness in software design.
The technical exploitation of this vulnerability occurs when a remote attacker crafts a specially formatted message containing malformed ASCII characters that the AIM client cannot properly handle during its parsing routine. When the vulnerable client receives such a message, it typically crashes or becomes unresponsive, effectively causing a denial of service for the targeted user. The attack vector is particularly concerning because it requires no authentication or specialized privileges from the attacker, making it accessible to anyone capable of sending messages to the target user. This vulnerability demonstrates the critical importance of robust input sanitization and error handling in client applications, especially those handling untrusted data from network sources. The flaw operates at the application layer and specifically affects the message handling subsystem of the AIM client, where the parsing logic does not adequately account for edge cases or malformed data sequences.
The operational impact of this vulnerability extends beyond simple service disruption to potentially affect user productivity and communication reliability within the AIM ecosystem. Users experiencing this denial of service condition would be unable to receive messages or maintain their instant messaging sessions until the client is manually restarted. This vulnerability also highlights the broader security implications of inadequate error handling in client-side applications, where unhandled exceptions or malformed data can lead to complete application failure. From an attacker perspective, this represents a low-effort, high-impact method of disrupting communication services, as demonstrated by the ATT&CK framework's categorization of such techniques under privilege escalation and denial of service tactics. The vulnerability's persistence across different versions of the AIM client indicates a fundamental flaw in the software architecture that was not adequately addressed in the initial design phase.
Mitigation strategies for CVE-2000-0190 should focus on implementing comprehensive input validation and error handling mechanisms within the AIM client software. The most effective approach involves modifying the message parsing logic to properly sanitize and validate all incoming ASCII data before processing, including implementing proper bounds checking and character set validation. Security patches should include defensive programming practices such as try-catch blocks around message processing routines, ensuring that malformed data does not cause application crashes. Additionally, implementing rate limiting and message filtering mechanisms can help reduce the impact of potential attacks by limiting the number of malformed messages that can be processed within a given timeframe. Organizations should also consider network-level filtering solutions that can identify and block suspicious message patterns before they reach client applications. The vulnerability serves as a reminder of the importance of following secure coding practices and implementing proper defensive measures against malformed input data, particularly in applications that handle real-time communication protocols where reliability is paramount. This type of vulnerability has been addressed in modern security frameworks through the implementation of the principle of least privilege and comprehensive input validation as recommended by various security standards and best practices.