CVE-2017-7695 in BigTree
Summary
by MITRE
Unrestricted File Upload exists in BigTree CMS before 4.2.17: if an attacker uploads an 'xxx.php[space]' file, they could bypass a safety check and execute any code.
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Analysis
by VulDB Data Team • 11/28/2022
The vulnerability identified as CVE-2017-7695 represents a critical unrestricted file upload flaw in BigTree CMS versions prior to 4.2.17, demonstrating a significant security weakness that directly enables remote code execution. This vulnerability exploits a specific bypass technique where attackers can upload malicious files with filenames containing trailing spaces followed by php extensions, effectively circumventing built-in security mechanisms designed to prevent the execution of potentially harmful code. The flaw resides in the content management system's file validation process, which fails to properly sanitize filenames during the upload procedure, creating an exploitable gap in the application's security controls.
The technical implementation of this vulnerability stems from inadequate input validation and sanitization within the file upload functionality of BigTree CMS. When an attacker uploads a file named 'xxx.php ' (note the trailing space), the system's security checks may incorrectly identify the file as non-executable due to the space character, while the underlying operating system or web server processes the file with its original extension, allowing the php code to execute. This bypass mechanism aligns with common security bypass techniques documented in CWE-434, which specifically addresses insecure file upload vulnerabilities where applications fail to properly validate file extensions or handle special characters in filenames. The vulnerability demonstrates a classic case of improper validation leading to privilege escalation through malicious file execution.
The operational impact of this vulnerability extends beyond simple code execution to encompass full system compromise, as attackers can leverage this flaw to gain unauthorized access to the underlying server infrastructure. Once executed, the uploaded php files can be used to establish persistent backdoors, exfiltrate sensitive data, or perform additional malicious activities within the compromised environment. The vulnerability affects organizations using affected versions of BigTree CMS, potentially exposing databases, user credentials, and other sensitive information stored within the system. From an attacker perspective, this vulnerability represents a low-effort, high-impact vector for exploitation, as it requires minimal reconnaissance and can be automated through various attack frameworks, making it particularly dangerous in environments where CMS systems are widely deployed.
Organizations should immediately upgrade to BigTree CMS version 4.2.17 or later to remediate this vulnerability, as no effective workarounds exist for the specific bypass technique. The mitigation strategy must include comprehensive file validation at multiple layers including client-side, server-side, and filesystem-level checks to prevent similar vulnerabilities from occurring. Security teams should implement proper input sanitization procedures that normalize filenames and reject any suspicious patterns, including trailing spaces, multiple extensions, or unusual character sequences. This vulnerability also highlights the importance of following secure coding practices as outlined in the OWASP Top Ten and NIST guidelines, particularly in addressing file upload security controls and implementing proper file type validation. Organizations should also consider implementing web application firewalls and intrusion detection systems to monitor for suspicious upload activities, while conducting regular security assessments to identify similar vulnerabilities in other applications within their attack surface. The ATT&CK framework categorizes this vulnerability under T1190 for Exploit Public-Facing Application, emphasizing the need for proper patch management and application security hardening to prevent such exploitation techniques from succeeding.