CVE-2017-7881 in BigTree
Summary
by MITRE
BigTree CMS through 4.2.17 relies on a substring check for CSRF protection, which allows remote attackers to bypass this check by placing the required admin/developer/ URI within a query string in an HTTP Referer header. This was found in core/admin/modules/developer/_header.php and patched in core/inc/bigtree/admin.php on 2017-04-14.
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Analysis
by VulDB Data Team • 11/29/2022
The vulnerability identified as CVE-2017-7881 affects BigTree CMS versions through 4.2.17 and represents a critical security flaw in the content management system's cross-site request forgery protection mechanism. This weakness stems from an insufficient implementation of CSRF validation that relies on simple substring matching rather than robust pattern recognition. The vulnerability specifically targets the administrative functionality of the CMS, where access controls are meant to prevent unauthorized users from executing privileged actions. The flaw exists in the core administrative modules and was addressed in the bigtree/admin.php file on April 14, 2017, but only after the vulnerability had been publicly disclosed and exploited.
The technical implementation of this vulnerability demonstrates a classic case of inadequate input validation and security control enforcement. The CSRF protection mechanism in BigTree CMS was designed to verify that requests originated from legitimate administrative pages by checking the HTTP Referer header against expected URI patterns. However, the implementation used a simple substring search approach that could be easily circumvented by attackers who understood the security mechanism's limitations. By placing the required URI patterns within a query string parameter of the Referer header rather than as a direct path component, attackers could bypass the protection entirely. This approach exploits the fundamental flaw in substring-based validation logic where a partial match is accepted as sufficient verification, even when the match occurs within a larger string context.
The operational impact of this vulnerability is significant and potentially devastating for organizations using affected BigTree CMS versions. Attackers who successfully exploit this flaw can bypass administrative access controls and gain unauthorized access to privileged functions within the CMS. This includes the ability to modify content, create or delete users, alter system configurations, and potentially escalate privileges to full administrative control. The vulnerability affects the core administrative modules, particularly those related to developer functionality, which often contain sensitive operations that should only be accessible to authorized administrators. The bypass mechanism is particularly dangerous because it can be executed remotely without requiring authentication credentials, making it an attractive target for automated exploitation tools.
The vulnerability aligns with CWE-352, which describes Cross-Site Request Forgery (CSRF) weaknesses in software applications. This classification indicates that the flaw represents a fundamental breakdown in the application's security controls for preventing unauthorized actions. From an attacker's perspective, this vulnerability maps to multiple ATT&CK techniques including T1078 for valid accounts and T1566 for phishing, as attackers can leverage this bypass to gain administrative access and then potentially use that access for further compromise. The attack surface is particularly concerning because it affects the administrative interface, which typically contains the most sensitive and powerful functions within a CMS. Organizations should note that this vulnerability demonstrates the importance of robust input validation and proper security control implementation, particularly when dealing with access control mechanisms that rely on HTTP headers for verification.
Mitigation strategies for this vulnerability require immediate patching of affected systems to the corrected version released on April 14, 2017, which addressed the substring validation issue in the bigtree/admin.php file. Organizations should also implement additional security measures including enhanced monitoring of HTTP Referer headers, implementing more robust CSRF token validation mechanisms, and ensuring that administrative access is protected through multiple layers of authentication. Security teams should conduct thorough vulnerability assessments of all BigTree CMS installations to identify potential exploitation attempts and implement proper access controls. The incident highlights the critical importance of not relying solely on header-based validation for security decisions and emphasizes the need for comprehensive security testing of access control mechanisms before deployment.