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Threat Model Analysis for matrix-org/synapse

Threat: Malicious Federation Event Injection

  • Threat: Malicious Federation Event Injection
    • Description: An attacker on a federated homeserver crafts a specially formatted Matrix event (e.g., a room message, state event, or presence update) containing malicious payloads. This payload could exploit vulnerabilities in how Synapse parses, validates, or processes the event data. The attacker sends this event to a room where the target Synapse server is participating.
    • Impact:
      • Remote Code Execution (RCE) on the Synapse server.
      • Denial of Service (DoS) by crashing the Synapse process or consuming excessive resources.
      • Data corruption or modification within the Synapse database.
      • Information disclosure (leaking sensitive data).
      • Client-side attacks if the malicious event is relayed to vulnerable clients.
    • Affected Synapse Component:
      • synapse.federation.federation_base: Core federation handling logic.
      • synapse.events.builder: Event building and validation.
      • synapse.events.persistence: Event storage and retrieval.
      • Specific event handlers within synapse.handlers (e.g., synapse.handlers.message, synapse.handlers.state).
      • Any modules involved in parsing specific event content types (e.g., media processing libraries).
    • Risk Severity: Critical (if RCE is possible), High (otherwise).
    • Mitigation Strategies:
      • Developer: Implement rigorous input validation and sanitization for all fields within incoming federated events. Use a strict schema and reject any events that do not conform. Fuzz test event parsing and handling code.
      • Developer: Employ memory-safe languages and coding practices to prevent buffer overflows and other memory corruption vulnerabilities.
      • Developer: Isolate event processing as much as possible (e.g., using sandboxing or separate processes).
      • Administrator: Keep Synapse updated to the latest version to receive security patches.
      • Administrator: Monitor federation traffic for anomalies and unusual event types.
      • Administrator: Consider using a Web Application Firewall (WAF) configured to understand Matrix event structures (challenging but potentially effective).

Threat: Backfilling DoS/Data Exfiltration

  • Threat: Backfilling DoS/Data Exfiltration
    • Description: A malicious homeserver sends a large number of backfill requests to the target Synapse server, requesting a significant amount of historical room data. This can overwhelm the server's resources (DoS) or, if access controls are weak, allow the attacker to exfiltrate large amounts of data they shouldn't have access to.
    • Impact:
      • Denial of Service (DoS) due to resource exhaustion (CPU, memory, database).
      • Data exfiltration of historical room data if access controls are insufficient.
      • Performance degradation for legitimate users.
    • Affected Synapse Component:
      • synapse.federation.federation_client: Handles outgoing federation requests.
      • synapse.federation.federation_server: Handles incoming federation requests.
      • synapse.storage.data_stores.main.room: Database interactions related to room data.
      • synapse.handlers.federation: Federation-specific handlers.
    • Risk Severity: High
    • Mitigation Strategies:
      • Developer: Implement rate limiting on backfill requests, both globally and per-homeserver.
      • Developer: Enforce strict access control checks before fulfilling backfill requests. Verify that the requesting server has the necessary permissions to access the requested data.
      • Administrator: Monitor backfill request rates and data volumes. Set alerts for suspicious activity.
      • Administrator: Configure appropriate resource limits for Synapse (CPU, memory, database connections).

Threat: Media Processing RCE

  • Threat: Media Processing RCE
    • Description: An attacker uploads a specially crafted media file (image, video, audio) designed to exploit a vulnerability in the media processing libraries used by Synapse (e.g., ImageMagick, FFmpeg, libwebp). These libraries are often complex and have a history of vulnerabilities.
    • Impact:
      • Remote Code Execution (RCE) on the Synapse server.
      • Denial of Service (DoS) by crashing the media processing component.
      • Information disclosure.
    • Affected Synapse Component:
      • synapse.media.thumbnailer: Handles thumbnail generation.
      • synapse.rest.media.v1.media_repository: Handles media uploads and downloads.
      • External media processing libraries (e.g., ImageMagick, FFmpeg, libwebp).
    • Risk Severity: Critical
    • Mitigation Strategies:
      • Developer: Keep media processing libraries absolutely up-to-date. Monitor security advisories for these libraries closely.
      • Developer: Run media processing in a highly restricted, sandboxed environment (e.g., using a separate process with minimal privileges, a container, or a virtual machine).
      • Developer: Implement strict input validation on media files before passing them to processing libraries. Check file types, sizes, and other metadata.
      • Developer: Consider using a dedicated media processing service separate from the main Synapse instance, further isolating potential vulnerabilities.
      • Administrator: Configure resource limits for media processing to prevent DoS attacks.
      • Administrator: Limit the types and sizes of media files that can be uploaded.

Threat: Database Injection

  • Threat: Database Injection
    • Description: An attacker exploits a vulnerability in how Synapse constructs SQL queries to inject malicious SQL code into the database. This could occur through any input field that is not properly sanitized before being used in a database query, potentially including federated data, user input, or API requests.
    • Impact:
      • Data exfiltration (reading sensitive data from the database).
      • Data modification (altering or deleting data).
      • Denial of Service (DoS) by causing database errors or consuming excessive resources.
      • Potentially Remote Code Execution (RCE) depending on the database configuration and the nature of the injection.
    • Affected Synapse Component:
      • synapse.storage: All database interaction modules.
      • Any handler that interacts with the database (synapse.handlers.*).
    • Risk Severity: High (Critical if RCE is possible)
    • Mitigation Strategies:
      • Developer: Use parameterized queries (prepared statements) exclusively for all database interactions. Never construct SQL queries by concatenating strings with user-supplied data.
      • Developer: Implement strict input validation and sanitization for all data that might be used in database queries.
      • Developer: Regularly review database interaction code for potential injection vulnerabilities.
      • Administrator: Keep the database server software (e.g., PostgreSQL) updated.
      • Administrator: Configure the database user with the least privilege necessary. Do not use a superuser account for Synapse.
      • Administrator: Enable database query logging and monitor for suspicious queries.