CVE-2019-16699 in sr_freecap Extension
Summary
by MITRE
The sr_freecap (aka freeCap CAPTCHA) extension 2.4.5 and below and 2.5.2 and below for TYPO3 fails to sanitize user input, which allows execution of arbitrary Extbase actions, resulting in Remote Code Execution.
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Analysis
by VulDB Data Team • 10/18/2019
The vulnerability identified as CVE-2019-16699 affects the sr_freecap CAPTCHA extension for TYPO3 content management systems, specifically versions 2.4.5 and below as well as 2.5.2 and below. This represents a critical security flaw that stems from inadequate input sanitization within the extension's handling of user-provided data. The vulnerability exists within the Extbase framework component of TYPO3, which is designed to facilitate rapid development of web applications. When users interact with the CAPTCHA functionality, the extension fails to properly validate or sanitize incoming parameters that are intended for processing within the Extbase action framework. This oversight creates a pathway for malicious actors to manipulate the extension's behavior by injecting crafted input that bypasses normal security controls. The vulnerability's impact extends beyond simple data manipulation, as it enables full remote code execution capabilities through the exploitation of the Extbase action invocation mechanism.
The technical exploitation of this vulnerability occurs through the manipulation of input parameters that are passed to Extbase controllers within the TYPO3 environment. When the sr_freecap extension processes user input, it fails to implement proper sanitization measures that would normally validate and filter data before it reaches the action execution layer. This allows attackers to inject malicious parameters that can trigger unintended Extbase actions, effectively providing a backdoor into the application's execution flow. The vulnerability operates at the intersection of input validation failures and action invocation mechanisms, creating a dangerous combination where user-supplied data can directly influence the execution path of the application. The flaw specifically targets the extension's handling of CAPTCHA-related parameters, but due to the lack of proper sanitization, attackers can leverage this weakness to execute arbitrary code within the context of the web server running TYPO3. This type of vulnerability is classified under CWE-20, which represents improper input validation, and aligns with ATT&CK technique T1059.001 for command and script injection.
The operational impact of CVE-2019-16699 is severe and far-reaching for organizations using affected TYPO3 installations. Successful exploitation enables attackers to gain complete control over the web server hosting the TYPO3 application, allowing them to execute arbitrary commands, access sensitive data, modify content, and potentially establish persistence within the environment. The vulnerability can be exploited remotely without requiring authentication, making it particularly dangerous as it can be leveraged by attackers from anywhere on the internet. Organizations may face significant consequences including data breaches, service disruption, and potential regulatory violations depending on the nature of the data processed by the affected systems. The attack surface is broad as any user who interacts with the CAPTCHA functionality could potentially trigger the vulnerability, and the impact extends to the entire TYPO3 installation since the exploitation occurs at the framework level rather than just the extension level. This vulnerability essentially provides attackers with a powerful foothold that can be used to escalate privileges and move laterally within the network infrastructure.
Mitigation strategies for CVE-2019-16699 primarily focus on immediate remediation through version updates to the sr_freecap extension. Organizations should upgrade to versions 2.5.3 or later, which contain the necessary input sanitization fixes. Additionally, system administrators should implement network-level protections such as web application firewalls that can detect and block malicious parameter injection attempts. The implementation of proper input validation measures at the application level should be enforced, ensuring that all user-provided data undergoes rigorous sanitization before being processed by any framework components. Security monitoring should be enhanced to detect unusual patterns in CAPTCHA-related requests that might indicate exploitation attempts. Organizations should also consider implementing principle of least privilege controls, limiting the capabilities of the web server account and restricting file system access to only necessary components. Regular security assessments and vulnerability scanning should be conducted to identify similar issues within other TYPO3 extensions, as this vulnerability pattern may exist in other components of the TYPO3 ecosystem. The fix addresses the root cause by implementing proper parameter validation and ensuring that Extbase actions are only invoked with sanitized and expected input parameters.