CVE-2009-4875 in FCKeditor.Java
Summary
by MITRE
FCKeditor.Java 2.4 allows remote attackers to cause a denial of service (infinite loop) via a malformed request parameter that contains "ctrl" characters.
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Analysis
by VulDB Data Team • 09/14/2021
The vulnerability identified as CVE-2009-4875 affects FCKeditor.Java version 2.4 and represents a significant denial of service weakness that can be exploited by remote attackers to disrupt system availability. This issue stems from the editor's inadequate handling of malformed request parameters containing control characters, specifically those with "ctrl" designation. The vulnerability manifests when the application processes input that includes control characters, leading to an infinite loop condition that consumes system resources and prevents legitimate operations from completing. Such a flaw represents a classic example of insufficient input validation and error handling within web applications.
The technical implementation of this vulnerability exploits the way FCKeditor.Java processes user input parameters during request handling. When a malicious actor submits a request containing control characters within the parameter values, the editor's parsing mechanism fails to properly sanitize or reject these inputs. The control characters trigger an iterative processing loop within the application's code that lacks proper termination conditions, causing the system to enter an infinite loop state. This behavior aligns with CWE-835, which specifically addresses infinite loops in software implementations, and demonstrates how improper input validation can lead to resource exhaustion attacks. The vulnerability is particularly concerning because it requires no authentication or specialized privileges to exploit, making it accessible to any remote attacker who can submit requests to the affected system.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise system stability and availability. An attacker can maintain the denial of service condition for extended periods, consuming CPU cycles and memory resources that would otherwise be available for legitimate user requests. This type of attack can be particularly damaging in environments where FCKeditor.Java is used for content management or user-generated content processing, as it can effectively shut down critical application functionality. The vulnerability also presents a risk to broader system availability since the infinite loop can cause the application server to become unresponsive, potentially affecting other applications running on the same infrastructure. This scenario aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and demonstrates how seemingly minor input validation flaws can escalate into serious operational security concerns.
Mitigation strategies for CVE-2009-4875 should focus on implementing robust input validation and sanitization mechanisms within the FCKeditor.Java implementation. Organizations should ensure that all user-supplied parameters undergo strict validation before processing, with particular attention to control character filtering and rejection. The recommended approach includes implementing comprehensive input sanitization routines that either remove or properly escape control characters from request parameters before they are processed by the editor component. Additionally, system administrators should consider implementing rate limiting and connection throttling mechanisms to prevent sustained exploitation attempts. The fix should also incorporate proper error handling and timeout mechanisms to prevent the application from entering indefinite processing states. Organizations should also evaluate their broader security posture and consider implementing web application firewalls or intrusion prevention systems that can detect and block malformed requests containing control characters. Regular security assessments and code reviews should be conducted to identify similar input validation weaknesses that could be exploited in similar fashion.