CVE-2007-3308 in Simple Machines
Summary
by MITRE
Simple Machines Forum (SMF) 1.1.2 uses a concatenation method with insufficient randomization when creating a WAV file CAPTCHA, which allows remote attackers to pass the CAPTCHA test via an automated brute-force attack.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 09/04/2018
The vulnerability identified as CVE-2007-3308 affects Simple Machines Forum version 1.1.2 and represents a critical weakness in the forum's CAPTCHA implementation that undermines its primary security purpose. This issue stems from the forum's use of concatenation methods when generating WAV file CAPTCHA audio challenges, creating a predictable and exploitable pattern that adversaries can easily bypass through automated means. The flaw fundamentally compromises the integrity of the CAPTCHA system, which is designed to distinguish between human users and automated bots by presenting challenges that are difficult for machines to solve but manageable for humans.
The technical root cause of this vulnerability lies in the insufficient randomization of the concatenation process used to create audio CAPTCHA files. When generating WAV files for CAPTCHA challenges, the system combines multiple audio segments without proper entropy injection, resulting in a deterministic sequence that can be reverse-engineered or systematically brute-forced by automated tools. This weakness directly relates to CWE-330, which addresses insufficient randomness in security-critical operations, and represents a classic example of poor cryptographic implementation where predictable patterns undermine security controls. The concatenation method essentially creates a reproducible audio signature that attackers can learn and replicate through automated brute-force approaches.
The operational impact of this vulnerability extends beyond simple bypass of security measures, as it enables attackers to automate forum registration, posting, and other user activities that should be restricted to legitimate human users. This opens the door to spam flooding, automated account creation for malicious purposes, and potential exploitation of other forum features through bot networks. The vulnerability affects the fundamental security model of the forum by allowing unauthorized access to user registration and content posting capabilities, potentially leading to data corruption, spam distribution, and service disruption. Attackers can systematically work through CAPTCHA challenges without human intervention, making this a particularly dangerous weakness for online communities that rely on CAPTCHA to maintain their integrity and prevent automated abuse.
Mitigation strategies for this vulnerability require immediate implementation of cryptographic-grade randomization in the CAPTCHA generation process, ensuring that each audio challenge contains sufficient entropy to prevent pattern recognition or brute-force attacks. The system should replace the current concatenation method with a properly randomized approach that incorporates high-quality random number generators and ensures that each CAPTCHA audio file is unique and unpredictable. Organizations should also implement additional security layers such as rate limiting, IP address monitoring, and behavioral analysis to detect and prevent automated abuse patterns. This vulnerability highlights the importance of proper entropy management in security implementations and aligns with ATT&CK technique T1213, which covers data from information repositories, emphasizing the need for robust protection of authentication mechanisms and CAPTCHA systems against automated attacks. The fix must address both the immediate cryptographic weakness in the audio generation process and establish monitoring capabilities to detect potential exploitation attempts.