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attack-surface.md

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Attack Surface Analysis for phacility/phabricator

Attack Surface: Cross-Site Scripting (XSS) via Markdown Rendering

  • Description: Injection of malicious scripts into web pages viewed by other users through vulnerabilities in Markdown and custom markup rendering.
  • Phabricator Contribution: Phabricator's core functionality relies on Markdown and its custom markup for user-generated content. Weaknesses in parsing and sanitizing these markups are direct Phabricator vulnerabilities.
  • Example: Malicious Javascript embedded in a Markdown comment within a Maniphest task executes when viewed by another user, potentially stealing session cookies.
  • Impact: Account compromise, data theft, defacement, redirection to malicious sites.
  • Risk Severity: High
  • Mitigation Strategies:
    • Developers:
      • Keep Phabricator Updated: Regularly update Phabricator to the latest version to patch known XSS vulnerabilities in Markdown rendering.
      • Content Security Policy (CSP): Implement and strictly configure Phabricator's CSP to limit script sources and mitigate XSS impact.
      • Input Sanitization and Output Encoding: Ensure robust sanitization of user inputs and proper output encoding during Markdown rendering to neutralize malicious scripts.
      • Security Audits: Conduct regular security audits and penetration testing focusing on Markdown and custom markup rendering to identify and fix potential XSS vectors.

Attack Surface: Authorization Bypass via Insecure Direct Object References (IDOR)

  • Description: Unauthorized access to resources by directly manipulating object identifiers (IDs) due to insufficient authorization checks in Phabricator's access control.
  • Phabricator Contribution: Phabricator's architecture relies on object IDs for accessing tasks, revisions, and other entities. Weak authorization checks when accessing objects via IDs are a direct Phabricator vulnerability.
  • Example: A user without permission to view a Differential revision (D123) directly accesses /D123 and gains unauthorized access because Phabricator fails to properly validate their permissions based on the revision ID.
  • Impact: Unauthorized access to sensitive code, project information, and data. Potential privilege escalation.
  • Risk Severity: High
  • Mitigation Strategies:
    • Developers:
      • Enforce Authorization Checks: Implement mandatory authorization checks in Phabricator's code whenever accessing resources based on object IDs.
      • Access Control Lists (ACLs) / Policies: Utilize Phabricator's built-in ACLs and policy mechanisms to define and rigorously enforce permissions for all object types.
      • Opaque Identifiers: Where possible, avoid exposing direct internal object IDs in URLs. Consider using opaque or hashed identifiers to obscure direct object references.
      • Authorization Testing: Perform thorough authorization testing for all functionalities, especially those involving object access via IDs, to identify and rectify IDOR vulnerabilities.

Attack Surface: File Upload Vulnerabilities leading to Remote Code Execution

  • Description: Exploiting Phabricator's file upload features to upload and execute malicious code on the server due to inadequate file validation and handling.
  • Phabricator Contribution: Phabricator's modules like Maniphest and Differential allow file uploads. Insufficient file validation and insecure storage practices within Phabricator directly contribute to this attack surface.
  • Example: An attacker uploads a PHP web shell disguised as an image through a Maniphest task's file upload. If Phabricator doesn't properly validate the file and stores it in a web-accessible location, the attacker can execute arbitrary PHP code on the server by accessing the web shell URL.
  • Impact: Remote code execution, full server compromise, data breach, denial of service.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Developers:
      • Strict File Type Validation: Implement robust file type validation based on file content (magic numbers) and not solely on file extensions within Phabricator's file upload handling logic.
      • Secure File Storage: Store uploaded files outside the web root directory to prevent direct execution via web requests. Configure Phabricator's file storage settings accordingly.
      • Web Server Configuration: Configure the web server (e.g., Apache, Nginx) to prevent script execution within the file upload directory using directives like .htaccess or server configuration blocks.
      • File Size Limits: Implement and enforce file size limits in Phabricator to prevent denial of service attacks through excessively large file uploads.
      • Malware Scanning: Integrate malware scanning of uploaded files using antivirus or anti-malware solutions to detect and block malicious uploads.

Attack Surface: API Authentication and Authorization Flaws

  • Description: Weaknesses in Phabricator's API authentication and authorization mechanisms, allowing unauthorized access or actions via the API.
  • Phabricator Contribution: Phabricator provides a comprehensive API. Vulnerabilities in how Phabricator manages API keys, enforces access control, and handles rate limiting are direct API security flaws within Phabricator itself.
  • Example: A leaked API key allows an attacker to bypass web interface restrictions and access sensitive data or modify configurations directly through the API, or lack of API rate limiting allows brute-force attacks.
  • Impact: Data breach, unauthorized data modification, denial of service, account takeover.
  • Risk Severity: High
  • Mitigation Strategies:
    • Developers:
      • Secure API Key Management: Implement secure generation, storage, and rotation of Phabricator API keys. Avoid default or weak API key generation methods.
      • API Authentication Enforcement: Mandate strong authentication for all Phabricator API endpoints.
      • Granular API Authorization: Implement fine-grained authorization controls for API access within Phabricator, ensuring users and applications only have access to necessary API resources and actions based on their roles and permissions.
      • API Rate Limiting: Implement API rate limiting and throttling within Phabricator to prevent abuse, brute-force attacks, and denial of service attempts targeting the API.
      • HTTPS for API Communication: Enforce HTTPS for all API communication to protect API keys and sensitive data transmitted over the network.
      • API Access Auditing: Regularly audit Phabricator API access logs to monitor for suspicious activity and detect potential unauthorized access or misuse.