CVE-2016-3166 in Drupal
Summary
by MITRE
CRLF injection vulnerability in the drupal_set_header function in Drupal 6.x before 6.38, when used with PHP before 5.1.2, allows remote attackers to inject arbitrary HTTP headers and conduct HTTP response splitting attacks by leveraging a module that allows user-submitted data to appear in HTTP headers.
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Analysis
by VulDB Data Team • 10/05/2018
The CVE-2016-3166 vulnerability represents a critical CRLF injection flaw in Drupal 6.x versions prior to 6.38, specifically when operating with PHP versions before 5.1.2. This vulnerability resides within the drupal_set_header function, which serves as a core component for setting HTTP headers in Drupal applications. The flaw exploits the absence of proper input sanitization when processing user-submitted data that gets incorporated into HTTP header values, creating a pathway for malicious actors to inject arbitrary HTTP headers into responses. The vulnerability is particularly dangerous because it enables HTTP response splitting attacks, where an attacker can inject malicious headers that manipulate the HTTP response structure. This issue is classified under CWE-113, which specifically addresses improper neutralization of CRLF characters in HTTP headers, making it a direct descendant of well-known header injection vulnerabilities. The attack vector requires a module that allows user-submitted data to appear in HTTP headers, which is common in content management systems where user input is processed and displayed in various contexts. When exploited, this vulnerability allows attackers to manipulate HTTP responses by injecting carriage return line feed sequences that break the standard HTTP response format.
The operational impact of CVE-2016-3166 extends beyond simple header injection, as it enables sophisticated attack patterns that can compromise web application security and user privacy. Attackers can leverage this vulnerability to perform session hijacking by injecting Set-Cookie headers that manipulate user sessions, or to conduct cache poisoning attacks by injecting Cache-Control headers that manipulate browser caching behavior. The vulnerability also enables open redirect attacks where attackers can inject Location headers to redirect users to malicious websites, and cross-site scripting attacks by injecting Content-Type headers that alter how browsers interpret content. From an ATT&CK framework perspective, this vulnerability maps to T1190 - Exploit Public-Facing Application, and T1071.005 - Application Layer Protocol: Web Protocols, as it exploits weaknesses in web application header handling. The vulnerability's exploitation capability is amplified by the fact that it requires minimal privileges and can be executed through standard user input mechanisms, making it particularly attractive to threat actors seeking to compromise Drupal installations. The specific PHP version constraint of before 5.1.2 indicates that this vulnerability was a legacy issue that persisted in older Drupal deployments where modern security patches had not been applied.
Mitigation strategies for CVE-2016-3166 focus on immediate patching and architectural defenses to prevent header injection attacks. The primary recommendation involves upgrading to Drupal 6.38 or later versions, which include proper input sanitization mechanisms that prevent CRLF sequences from being processed in HTTP headers. Organizations should also implement comprehensive input validation at multiple layers, including application-level filtering of user-submitted data that might appear in HTTP headers. Network-level defenses such as web application firewalls can provide additional protection by detecting and blocking CRLF injection patterns in HTTP requests. Security teams should conduct thorough vulnerability assessments to identify modules that might process user data in HTTP headers, as these components are particularly susceptible to exploitation. The implementation of proper header sanitization techniques, including the removal or encoding of CRLF characters from user input, should be enforced across all application components that handle HTTP response generation. Additionally, organizations should consider implementing header security policies that restrict the use of dynamic header values and enforce strict validation of all HTTP header content. From a compliance standpoint, this vulnerability highlights the importance of maintaining up-to-date software versions and implementing continuous security monitoring to detect and remediate similar issues before they can be exploited by malicious actors. The vulnerability also underscores the necessity of following security best practices such as the principle of least privilege and defense in depth to minimize the attack surface available to potential threat actors.