threat-modeling.md

Threat Model Analysis for signalapp/signal-server

Threat: Database Vulnerabilities Leading to Data Breach

• Description: An attacker could exploit vulnerabilities in the database system used by signal-server or in signal-server's database access layer to gain unauthorized access to the database. This could allow them to dump the entire database content, including messages, user profiles, and potentially keys.
• Impact: Mass compromise of user data, including message history, contact information, and potentially cryptographic keys. Severe privacy breach, loss of user trust, and potential legal repercussions.
• Affected Component: Database (e.g., PostgreSQL), Database Access Layer within signal-server.
• Risk Severity: Critical.
• Mitigation Strategies:
  • Developers: Regularly patch and update the database system to the latest secure versions. Implement strong database access controls and authentication within signal-server. Use parameterized queries or ORM to prevent SQL injection vulnerabilities in signal-server's database interactions. Encrypt data at rest in the database. Perform regular database security audits and vulnerability scans focusing on signal-server's database usage.

Threat: Server-Side Caching of Decrypted Data

• Description: If signal-server incorrectly implements server-side caching of decrypted message content, an attacker gaining access to the server or cache storage could retrieve this decrypted data. This is a fundamental design flaw for an end-to-end encrypted system.
• Impact: Exposure of decrypted message content. Complete compromise of end-to-end encryption promise. Severe privacy breach.
• Affected Component: Caching Module (if implemented within signal-server), Message Processing Module within signal-server.
• Risk Severity: Critical.
• Mitigation Strategies:
  • Developers: Absolutely avoid server-side decryption and caching of message content in signal-server. If caching is necessary for other data within signal-server, ensure it is encrypted at rest and in transit, with strict access controls and short cache lifetimes. Regularly audit signal-server code to ensure no accidental decryption and caching of message content occurs.

Threat: Session Hijacking or Management Vulnerabilities

• Description: An attacker could exploit vulnerabilities in session management within signal-server (e.g., weak session identifiers generated by signal-server, session fixation vulnerabilities in signal-server's authentication flow) to steal or hijack user sessions. This would allow them to impersonate legitimate users without proper authentication.
• Impact: Account takeover, unauthorized access to messages and user data managed by signal-server, and ability to perform actions as the compromised user. Severe privacy and security breach.
• Affected Component: Session Management Module within signal-server, Authentication Module within signal-server.
• Risk Severity: Critical.
• Mitigation Strategies:
  • Developers: Use strong, cryptographically random session identifiers generated by signal-server. Implement secure session storage and transmission (HTTPS enforced by signal-server). Implement proper session expiration and invalidation within signal-server. Protect against session fixation and session hijacking attacks in signal-server's authentication logic (e.g., using HttpOnly and Secure flags for cookies if applicable). Regularly audit signal-server's session management logic.

Threat: Privilege Escalation within Server Components

• Description: An attacker who has gained initial access to signal-server (e.g., through a web application vulnerability in a component of signal-server, compromised credentials used to access signal-server's admin interface) could exploit vulnerabilities within signal-server components to escalate their privileges. This could allow them to gain administrative access to the signal-server instance.
• Impact: Full control over the signal-server instance, ability to access all data managed by signal-server, modify configurations of signal-server, and potentially compromise user accounts and message integrity. Catastrophic security breach.
• Affected Component: Various Server Components within signal-server, potentially related to authentication, authorization, or input handling within signal-server.
• Risk Severity: Critical.
• Mitigation Strategies:
  • Developers/Operators: Apply the principle of least privilege within signal-server's internal architecture. Implement secure coding practices in signal-server to prevent vulnerabilities that could lead to privilege escalation. Regularly perform security audits and penetration testing specifically targeting signal-server's internal components and privilege separation. Implement robust access control mechanisms within signal-server's configuration and administration interfaces.

Threat: API Vulnerabilities Exposing User Data

• Description: An attacker could exploit vulnerabilities in signal-server's API endpoints (e.g., insecure direct object references, broken authentication/authorization in signal-server's API logic, insufficient input validation in API handlers) to access user data without proper authorization. They could enumerate user IDs, access profile information, contact lists, group memberships, or message metadata by crafting malicious API requests to signal-server.
• Impact: Unauthorized access to user information managed by signal-server, potentially enabling targeted attacks, privacy breaches, and account enumeration.
• Affected Component: API Endpoints within signal-server, Authentication and Authorization Modules within signal-server, User Profile and Contact Management Modules within signal-server.
• Risk Severity: High.
• Mitigation Strategies:
  • Developers: Implement robust authentication and authorization mechanisms (e.g., OAuth 2.0, JWT) for signal-server's APIs. Thoroughly test API endpoints for authorization vulnerabilities within signal-server. Use input validation and output encoding in signal-server's API handlers to prevent injection attacks. Implement rate limiting in signal-server's API layer to prevent brute-force attacks. Conduct regular API security audits and penetration testing specifically targeting signal-server's APIs. Follow secure API design principles when developing signal-server's APIs.

Threat: Message Tampering in Transit or Storage (Server-Side)

• Description: An attacker with server access (e.g., compromised server hosting signal-server, insider threat with access to signal-server's infrastructure) could potentially modify messages as they are processed or stored by signal-server before delivery to the recipient. This could involve altering message content, sender/receiver information, or timestamps within signal-server's message handling logic.
• Impact: Compromise of message integrity, leading to misinformation, manipulation of communication, and loss of trust in the platform relying on signal-server.
• Affected Component: Message Processing Module within signal-server, Message Storage Module within signal-server.
• Risk Severity: High.
• Mitigation Strategies:
  • Developers: Implement robust input validation and output encoding throughout signal-server's message processing pipeline. Use cryptographic integrity checks (e.g., message authentication codes) on stored messages within signal-server. Adhere to secure coding practices in signal-server to prevent vulnerabilities that could allow message manipulation. Implement audit logging of message modifications within signal-server.

Threat: Denial of Service (DoS) Attacks Targeting Message Processing

• Description: An attacker could flood signal-server with a large volume of messages or specially crafted messages designed to consume excessive server resources (CPU, memory, network bandwidth) within signal-server's message processing components. This could overwhelm the server and cause service disruption for legitimate users of the signal-server instance.
• Impact: Service unavailability of signal-server, preventing message delivery and communication. Business disruption and potential reputational damage for services relying on signal-server.
• Affected Component: Message Processing Module within signal-server, Network Communication handling within signal-server, Resource Management within signal-server.
• Risk Severity: High.
• Mitigation Strategies:
  • Developers/Operators: Implement rate limiting on message submission within signal-server. Use input validation in signal-server to prevent processing of malicious messages. Implement robust resource management and monitoring for the signal-server instance. Deploy DDoS mitigation techniques (e.g., traffic filtering, load balancing) in front of the signal-server instance.

Threat: Database Overload or Failure

• Description: High message volume processed by signal-server, inefficient database queries performed by signal-server, database vulnerabilities, or resource exhaustion in the database server supporting signal-server could lead to database overload or failure. This could cause service unavailability of signal-server and potentially data loss if backups are insufficient.
• Impact: Service outage of signal-server, data loss if database backups are inadequate. Business disruption and potential reputational damage for services relying on signal-server.
• Affected Component: Database (e.g., PostgreSQL) used by signal-server, Database Access Layer within signal-server.
• Risk Severity: High.
• Mitigation Strategies:
  • Developers/Operators: Optimize database performance for signal-server's queries through query optimization, indexing, and database tuning. Implement capacity planning and scaling to handle expected message volumes for signal-server. Implement robust database monitoring and alerting for the database supporting signal-server. Regularly perform database backups and test disaster recovery plans for the database used by signal-server. Consider database clustering for redundancy and high availability for the database supporting signal-server.