threat-modeling.md

Threat Model Analysis for carrierwaveuploader/carrierwave

Threat: Bypassing File Type Validation

• Description: An attacker crafts or renames a malicious file to bypass server-side file type checks implemented using Carrierwave's content_type_whitelist or content_type_blacklist. They upload this file hoping it will be processed or served as a legitimate file type, potentially leading to exploitation.
• Impact: Remote Code Execution (RCE) if executed on server, Cross-Site Scripting (XSS) if served to clients, data corruption, system compromise.
• Carrierwave Component Affected: Uploader module, content_type_whitelist, content_type_blacklist validators.
• Risk Severity: Critical
• Mitigation Strategies:
  • Use server-side file type validation with content_type_whitelist and content_type_blacklist.
  • Verify file content using magic number analysis in addition to MIME type checks.
  • Avoid relying solely on client-side validation.
  • Consider using file scanning tools to detect malicious content.

Threat: Malicious File Content (Beyond File Type)

• Description: An attacker uploads files that are of allowed types but contain malicious payloads within them (e.g., polyglot files, embedded scripts in images, macro-enabled documents, viruses). These payloads can be triggered when the file is processed, opened, or served by the application or its users.
• Impact: Remote Code Execution (RCE), Cross-Site Scripting (XSS), data breach, malware infection, system compromise.
• Carrierwave Component Affected: Uploader module, file processing and storage mechanisms, application logic handling uploaded files.
• Risk Severity: Critical
• Mitigation Strategies:
  • Implement virus scanning and malware detection on all uploaded files.
  • Sanitize and process files in a secure environment (sandboxing).
  • Be cautious when processing or serving files of types known to be susceptible to embedded exploits.

Threat: Publicly Accessible Storage Location

• Description: Storage backends configured with Carrierwave (e.g., S3 buckets, local directories) are misconfigured to be publicly accessible. Attackers can directly access and download all uploaded files without authorization, leading to data breaches.
• Impact: Data breach, unauthorized access to sensitive information, privacy violations, reputational damage.
• Carrierwave Component Affected: Storage configuration (e.g., fog, file storage configurations).
• Risk Severity: Critical
• Mitigation Strategies:
  • Properly configure storage backend permissions to restrict public access.
  • Use private S3 buckets or secure file system permissions.
  • Regularly audit storage backend configurations.

Threat: Insecure Storage Directory (Web-Accessible)

• Description: Uploaded files are stored in a directory directly accessible by the web server (e.g., within the public directory) due to misconfiguration or default Carrierwave settings. Attackers can directly access files via their URLs, bypassing application-level authorization.
• Impact: Unauthorized file access, data breach, privacy violations.
• Carrierwave Component Affected: Storage configuration (e.g., file storage path), Uploader module default path settings.
• Risk Severity: High
• Mitigation Strategies:
  • Store uploaded files outside the web server's document root.
  • Configure Carrierwave to use a storage location that is not directly web-accessible.
  • Serve files through application logic with proper authorization checks.

Threat: Image Processing Vulnerabilities (ImageMagick, etc.)

• Description: Carrierwave's image processing features rely on libraries like ImageMagick or MiniMagick. These libraries may have known vulnerabilities that can be exploited through crafted image files uploaded via Carrierwave. Attackers can trigger these vulnerabilities, potentially leading to Remote Code Execution (RCE) or Denial of Service (DoS).
• Impact: Remote Code Execution (RCE), Denial of Service (DoS), system compromise.
• Carrierwave Component Affected: MiniMagick or ImageMagick processors within Uploader module, process method.
• Risk Severity: Critical
• Mitigation Strategies:
  • Keep image processing libraries (ImageMagick, MiniMagick) up-to-date with the latest security patches.
  • Sanitize image files before processing.
  • Consider using safer image processing alternatives if available.
  • Implement sandboxing for image processing tasks.

Threat: Exploits in File Format Parsers

• Description: If Carrierwave is used to process various file formats beyond images, vulnerabilities in libraries used to parse these formats (e.g., PDF, Office documents) can be exploited through malicious files uploaded via Carrierwave. Attackers can trigger these vulnerabilities, leading to RCE or other security issues.
• Impact: Remote Code Execution (RCE), Denial of Service (DoS), system compromise, data exfiltration.
• Carrierwave Component Affected: Application logic processing files, external libraries used for file parsing (indirectly related to Carrierwave usage).
• Risk Severity: Critical
• Mitigation Strategies:
  • Keep all file parsing libraries up-to-date with security patches.
  • Sanitize files before processing.
  • Implement sandboxing for file processing tasks.
  • Use robust and well-maintained parsing libraries.

Threat: Unrestricted File Upload Size

• Description: An attacker uploads extremely large files via Carrierwave to exhaust server disk space, storage quotas, or server resources (memory, bandwidth). This can lead to denial of service for legitimate users.
• Impact: Denial of Service (DoS), increased infrastructure costs, application instability.
• Carrierwave Component Affected: Uploader module, specifically file processing and storage mechanisms.
• Risk Severity: High
• Mitigation Strategies:
  • Implement maximum_size validation in Carrierwave uploaders.
  • Enforce infrastructure-level limits on request size and storage quotas.
  • Monitor disk space and resource usage.

Threat: Filename Injection & Path Traversal

• Description: An attacker manipulates the uploaded filename to include path traversal sequences (../) or special characters when using Carrierwave. This can cause the file to be stored outside the intended directory, potentially overwriting system files or accessing restricted areas.
• Impact: File overwrite, unauthorized file access, potential system compromise, data loss.
• Carrierwave Component Affected: Uploader module, filename method, storage mechanisms.
• Risk Severity: High
• Mitigation Strategies:
  • Sanitize filenames using Carrierwave's built-in sanitization or custom sanitization logic.
  • Restrict allowed characters in filenames.
  • Ensure generated storage paths are secure and prevent traversal.

Threat: Resource Exhaustion During Processing

• Description: Processing very large or complex files uploaded via Carrierwave can consume excessive server resources (CPU, memory), leading to resource exhaustion and Denial of Service (DoS). Attackers can intentionally upload such files to overload the server.
• Impact: Denial of Service (DoS), application slowdown, server instability.
• Carrierwave Component Affected: Uploader module, process method, file processing mechanisms.
• Risk Severity: High
• Mitigation Strategies:
  • Implement resource limits for file processing tasks (timeouts, memory limits, CPU limits).
  • Queue processing tasks to prevent overloading the server.
  • Use background processing for resource-intensive operations.

Threat: Insecure Default Configurations

• Description: Relying on default Carrierwave configurations without proper review and customization can leave security gaps. Default settings for storage paths, access control, or validation might not be secure and could expose vulnerabilities.
• Impact: Various vulnerabilities depending on the insecure default configuration, potentially leading to data breaches, unauthorized access, or system compromise.
• Carrierwave Component Affected: Configuration settings across all Carrierwave modules and features.
• Risk Severity: High
• Mitigation Strategies:
  • Review and customize Carrierwave configurations to align with security best practices.
  • Explicitly configure storage locations, access control, validation rules, and filename sanitization.
  • Avoid relying on default settings without understanding their security implications.

Threat: Improper Use of Whitelists/Blacklists

• Description: Misusing or incompletely implementing whitelists or blacklists for file type validation in Carrierwave can lead to bypasses. Blacklists are inherently less secure, and incomplete whitelists can block legitimate file types while still allowing malicious ones.
• Impact: Bypassing file type validation, allowing malicious file uploads, potentially leading to security vulnerabilities.
• Carrierwave Component Affected: content_type_whitelist, content_type_blacklist validators in Uploader module.
• Risk Severity: High
• Mitigation Strategies:
  • Prefer using whitelists for allowed file types whenever possible.
  • Combine whitelists with content-based validation (magic numbers).
  • Regularly review and update whitelists to ensure they are comprehensive and accurate.