CVE-2019-9845 in Miniblog.Core
Summary
by MITRE
madskristensen Miniblog.Core through 2019-01-16 allows remote attackers to execute arbitrary ASPX code via an IMG element with a data: URL, because SaveFilesToDisk in Controllers/BlogController.cs writes a decoded base64 string to a file without validating the extension.
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Analysis
by VulDB Data Team • 08/29/2023
The vulnerability identified as CVE-2019-9845 affects the madskristensen Miniblog.Core blogging platform version 2019-01-16 and earlier, representing a critical server-side code execution flaw that enables remote attackers to inject and execute arbitrary ASPX code on affected systems. This vulnerability stems from inadequate input validation within the file upload and processing functionality of the blogging platform, specifically in the Controllers/BlogController.cs file where the SaveFilesToDisk method operates without proper extension validation. The flaw allows attackers to bypass normal security restrictions by leveraging the data: URL scheme within IMG elements, which when processed by the vulnerable application can result in malicious code execution on the server.
The technical implementation of this vulnerability exploits a fundamental security weakness in the application's file handling mechanism, where base64 encoded content is decoded and written to disk without proper validation of the file extension or content type. This creates a path traversal and code execution vector that directly violates security principles outlined in CWE-434, which addresses insecure file upload vulnerabilities. When an attacker constructs an IMG element containing a data: URL with base64 encoded malicious ASPX content, the vulnerable application decodes this content and writes it to disk as a file, effectively allowing arbitrary code execution on the server with the privileges of the web application. The vulnerability operates at the application layer and can be exploited through web-based attacks without requiring authentication or special privileges.
The operational impact of this vulnerability is severe and far-reaching, as it provides attackers with complete control over the affected server and its resources. Successful exploitation can lead to full system compromise, data theft, privilege escalation, and potential lateral movement within network environments. The vulnerability affects any system running vulnerable versions of Miniblog.Core, making it particularly dangerous in production environments where blogging platforms are exposed to external traffic. Attackers can leverage this vulnerability to establish persistent backdoors, exfiltrate sensitive information, or use the compromised server as a launch point for further attacks against other systems within the network perimeter. This aligns with tactics described in the MITRE ATT&CK framework under the T1059.001 technique for command and scripting interpreter, where adversaries execute code through web applications.
Mitigation strategies for CVE-2019-9845 must address both immediate remediation and long-term security hardening measures. The primary fix involves updating to a patched version of Miniblog.Core that implements proper file extension validation and content type checking before saving files to disk. Organizations should implement strict file validation that checks for allowed extensions, validates file content signatures, and sanitizes all user-provided input before processing. Additional protective measures include implementing web application firewalls to block suspicious data: URL patterns, restricting file upload capabilities to authenticated users only, and deploying proper input sanitization techniques. Security controls should also include monitoring for unusual file creation patterns and implementing least privilege principles for web application accounts to minimize potential damage from successful exploitation attempts.