CVE-2001-1421 in Instant Messenger
Summary
by MITRE
AOL Instant Messenger (AIM) 4.7 and earlier allows remote attackers to cause a denial of service (application crash) via a large number of different fonts followed by an HTML HR tag.
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Analysis
by VulDB Data Team • 11/15/2024
The vulnerability identified as CVE-2001-1421 represents a classic denial of service flaw affecting AOL Instant Messenger version 4.7 and earlier implementations. This weakness specifically targets the client-side rendering engine of AIM, which processes incoming messages containing formatted content. The vulnerability exploits a parsing inconsistency in how the application handles font specifications within HTML content, creating a scenario where malformed or excessively complex formatting can trigger application instability.
The technical mechanism behind this vulnerability involves the improper handling of HTML elements within AIM's message processing pipeline. When a remote attacker crafts a malicious message containing a large number of distinct font specifications followed by an HTML HR tag, the AIM client attempts to render this content by allocating memory resources proportional to the font variations specified. This excessive resource allocation, combined with the subsequent HTML processing, causes the application to consume excessive system resources and ultimately crash. The flaw manifests as a buffer overflow condition or memory exhaustion scenario that the application cannot properly handle during message rendering.
From an operational perspective, this vulnerability presents a significant risk to users of legacy AIM systems, as it requires no special privileges or authentication to exploit. The attack can be executed through simple message transmission, making it particularly dangerous in environments where AIM remains in use. The impact extends beyond individual user disruption to potentially affect broader communication networks, as multiple simultaneous attacks could overwhelm system resources and create cascading failures. This type of vulnerability aligns with CWE-129, which describes improper validation of array index values, and represents a form of resource exhaustion attack that can be categorized under the ATT&CK framework's privilege escalation and denial of service tactics.
The mitigation strategies for this vulnerability primarily involve immediate software updates and patches provided by AOL to address the parsing inconsistencies in the HTML rendering engine. Organizations should implement network-level filtering to block suspicious message content, particularly those containing excessive font specifications or malformed HTML elements. Additionally, system administrators should consider implementing application sandboxing techniques to isolate AIM processes and prevent complete application crashes from affecting system stability. Regular security assessments should verify that AIM clients are updated to versions that properly validate HTML content and implement proper resource management during message rendering. The vulnerability serves as a historical example of how legacy messaging applications can contain fundamental flaws in their content processing that require careful handling of user-provided data to prevent exploitation.