CVE-2005-2781 in FUDforum
Summary
by MITRE
The Avatar upload feature in FUD Forum before 2.7.0 does not properly verify uploaded files, which allows remote attackers to execute arbitrary PHP code via a file with a .php extension that contains image data followed by PHP code.
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Analysis
by VulDB Data Team • 06/09/2019
The vulnerability described in CVE-2005-2781 represents a critical security flaw in the FUD Forum software version 2.7.0 and earlier, where the avatar upload functionality fails to properly validate file types and contents. This weakness creates an avenue for remote attackers to bypass security measures and execute malicious code on the target system. The vulnerability specifically exploits the lack of proper file extension and content verification mechanisms within the avatar upload process, allowing attackers to upload files that appear to be image files but actually contain PHP code. The flaw stems from insufficient input validation and sanitization practices that permit files with .php extensions to be uploaded and subsequently executed by the web server, even when they are disguised as image files.
This vulnerability directly maps to CWE-434, which describes the weakness of allowing untrusted data to be uploaded to a web server and subsequently executed. The technical implementation of the flaw involves the web application's failure to perform comprehensive file validation checks that would normally verify both the file extension and the actual file content. Attackers can craft malicious files that begin with valid image headers followed by PHP code, fooling the system into treating them as legitimate images while actually executing the embedded code. The vulnerability exists because the application relies on the file extension alone for validation rather than implementing proper content inspection mechanisms. This approach is fundamentally flawed as it can be easily circumvented by renaming files to have .php extensions or by creating files where the PHP code is embedded within image data structures.
The operational impact of this vulnerability is severe and far-reaching, as it provides attackers with arbitrary code execution capabilities on the compromised system. Once successfully exploited, attackers can gain full control over the web server, potentially leading to data theft, system compromise, and further lateral movement within the network. The vulnerability enables attackers to upload backdoors, web shells, or other malicious payloads that can persist on the system and provide ongoing access. This type of vulnerability is particularly dangerous in forum environments where user-generated content is common, as it can be exploited by any user with avatar upload privileges. The attack vector is straightforward and effective, requiring minimal technical expertise to exploit, making it a high-risk vulnerability that could be leveraged for widespread damage.
Mitigation strategies for this vulnerability should focus on implementing comprehensive file validation and sanitization measures. The primary defense involves enforcing strict file type validation that checks both the file extension and the actual file content using proper MIME type detection and content analysis. Organizations should implement a whitelist approach for allowed file types, rejecting all uploads that do not conform to predefined security policies. Additionally, uploaded files should be stored in a separate directory from executable code and should not be directly accessible via the web server. The recommended approach includes implementing proper file validation libraries, using secure file handling practices, and ensuring that uploaded files are processed through proper content inspection mechanisms. This vulnerability highlights the critical importance of following secure coding practices and implementing defense-in-depth strategies, as outlined in the mitre ATT&CK framework under the execution and persistence categories. The vulnerability also emphasizes the need for regular security assessments and timely patch management to prevent exploitation of known security flaws.