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Mitigation Strategies Analysis for matrix-org/synapse

Mitigation Strategy: Implement Strict Federation Controls

1. Implement Strict Federation Controls

  • Mitigation Strategy: Strict Federation Controls (Domain Whitelisting/Blacklisting)
  • Description:
    1. Identify Trusted Domains: Determine the Matrix servers your Synapse instance needs to federate with.
    2. Configure federation_domain_whitelist: In your homeserver.yaml configuration file, set the federation_domain_whitelist option to a list of these trusted domains. Only federation requests from these domains will be accepted by Synapse.
    3. Alternatively, Configure federation_domain_blacklist: If whitelisting is impractical, use federation_domain_blacklist in homeserver.yaml to block known malicious or untrusted domains from federating with your Synapse instance.
    4. Regularly Review and Update: Periodically review and update the whitelist or blacklist in homeserver.yaml as trust relationships change.
    5. Restart Synapse: Restart the Synapse service for the configuration changes to take effect.
  • List of Threats Mitigated:
    • Federation Spam/Abuse (Medium - High): Prevents unwanted rooms, messages, and user reports from untrusted servers interacting with your Synapse instance.
    • Federation-Based DoS/DDoS (Medium): Limits the attack surface of your Synapse instance by restricting federation connections.
    • Exposure to Vulnerable Federated Servers (Medium): Reduces the risk of your Synapse instance interacting with vulnerable or malicious external servers.
  • Impact:
    • Federation Spam/Abuse (High): Significantly reduces spam and abuse originating from external Matrix servers on your Synapse instance.
    • Federation-Based DoS/DDoS (Medium): Moderately reduces the risk of federation-based DoS/DDoS attacks targeting your Synapse instance.
    • Exposure to Vulnerable Federated Servers (Medium): Moderately reduces risk to your Synapse instance, depending on the whitelist/blacklist comprehensiveness.
  • Currently Implemented:
    • Partially Implemented: Synapse provides federation_domain_whitelist and federation_domain_blacklist configuration options directly within homeserver.yaml.
    • Location: Configuration is done in the homeserver.yaml file of your Synapse instance.
  • Missing Implementation:
    • Proactive Whitelist Management within Synapse UI/API: Lack of built-in Synapse UI or Admin API for easier, dynamic management of the federation whitelist/blacklist.
    • Automated Domain Reputation Integration within Synapse: No direct integration within Synapse to automatically update the blacklist based on domain reputation services.

Mitigation Strategy: Rate Limit Federation Requests

2. Rate Limit Federation Requests

  • Mitigation Strategy: Federation Rate Limiting (Synapse Configuration)
  • Description:
    1. Identify Rate Limiting Parameters: Determine appropriate rate limits for federation requests to your Synapse instance based on its capacity and expected traffic.
    2. Configure Rate Limiting in homeserver.yaml: Utilize Synapse's rate limiting configuration options within the federation_client section of homeserver.yaml. This involves settings like max_federation_txn_lifetime_ms, federation_max_retries, and potentially custom rate limiting modules configurable in Synapse.
    3. Monitor Rate Limiting Effectiveness: Monitor Synapse logs and metrics related to federation rate limiting to ensure it is effective and not impacting legitimate federation traffic to your Synapse instance.
    4. Adjust Rate Limits via homeserver.yaml: Adjust rate limits in homeserver.yaml as needed based on observed traffic patterns and Synapse performance.
  • List of Threats Mitigated:
    • Federation-Based DoS/DDoS (High): Prevents malicious federated servers from overwhelming your Synapse instance with excessive requests.
    • Resource Exhaustion from Misbehaving Servers (Medium): Protects Synapse server resources from being consumed by misconfigured external servers sending excessive traffic.
  • Impact:
    • Federation-Based DoS/DDoS (High): Significantly reduces the impact of DoS/DDoS attacks originating from federated servers targeting your Synapse instance.
    • Resource Exhaustion from Misbehaving Servers (Medium): Moderately reduces resource exhaustion on your Synapse server.
  • Currently Implemented:
    • Partially Implemented: Synapse has built-in federation rate limiting capabilities configurable directly in homeserver.yaml.
    • Location: Configuration is primarily in homeserver.yaml within sections related to federation of your Synapse instance.
  • Missing Implementation:
    • Granular Rate Limiting within Synapse: Default Synapse rate limiting might lack granularity for specific federation request types or source servers. More advanced Synapse configurations or custom modules might be needed.
    • Adaptive Rate Limiting within Synapse Core: Lack of dynamic or adaptive rate limiting within Synapse core that automatically adjusts based on real-time traffic patterns.
    • Centralized Rate Limiting Management for Synapse Clusters: For Synapse clusters, managing rate limits across instances might lack centralized management tools within Synapse itself.

Mitigation Strategy: Validate Federated Events Thoroughly

3. Validate Federated Events Thoroughly

  • Mitigation Strategy: Strict Federated Event Validation (Synapse Feature)
  • Description:
    1. Enable Strict Validation in Synapse Configuration: Ensure that Synapse is configured to perform strict validation of incoming federated events. Verify configuration options related to event validation in homeserver.yaml of your Synapse instance.
    2. Verify Signature Verification is Enabled in Synapse: Confirm that Synapse is configured to verify signatures on federated events. This is a core security feature of Matrix federation handled by Synapse.
    3. Implement Robust Error Handling in Synapse: Ensure Synapse has robust error handling for invalid federated events. Invalid events should be rejected and logged by Synapse.
    4. Regularly Review Synapse Validation Logs: Monitor Synapse logs for event validation errors to identify issues with federated servers or potential attacks targeting your Synapse instance.
  • List of Threats Mitigated:
    • Federation-Based Injection Attacks (High): Prevents malicious servers from injecting malicious code or data into your Synapse instance through crafted events.
    • Data Corruption from Malicious Servers (Medium): Reduces the risk of data corruption in your Synapse instance caused by processing invalid events.
    • Denial of Service through Invalid Events (Medium): Prevents attackers from causing DoS to your Synapse instance by sending a flood of invalid events.
  • Impact:
    • Federation-Based Injection Attacks (High): Significantly reduces the risk of injection attacks targeting your Synapse instance via federation.
    • Data Corruption from Malicious Servers (Medium): Moderately reduces data corruption within Synapse.
    • Denial of Service through Invalid Events (Medium): Moderately reduces DoS risk to Synapse.
  • Currently Implemented:
    • Largely Implemented: Synapse has built-in event validation and signature verification as core federation features within its code.
    • Location: Core Synapse code handles event validation. Configuration in homeserver.yaml might influence the strictness.
  • Missing Implementation:
    • Advanced Content Sanitization within Synapse: While Synapse performs basic sanitization, more advanced techniques within Synapse might be needed for sophisticated injection attempts.
    • Context-Aware Validation within Synapse: Current Synapse validation is schema-based but could be enhanced with context-aware validation considering room/user state.

Mitigation Strategy: Rate Limit Client API Requests

4. Rate Limit Client API Requests

  • Mitigation Strategy: Client API Rate Limiting (Synapse Configuration)
  • Description:
    1. Identify API Endpoints to Rate Limit: Determine which Client-Server API endpoints of your Synapse instance are most vulnerable to abuse.
    2. Configure Rate Limiting in homeserver.yaml: Utilize Synapse's rate limiting configuration options within the client_api section of homeserver.yaml.
    3. Implement Different Rate Limits via homeserver.yaml: Configure different rate limits in homeserver.yaml for different API endpoints based on sensitivity and abuse potential within Synapse.
    4. Monitor Rate Limiting and Adjust via homeserver.yaml: Monitor Synapse logs and metrics related to client API rate limiting and adjust settings in homeserver.yaml as needed.
    5. Consider CAPTCHA or Progressive Challenges in Application Layer: For high-risk endpoints, consider implementing CAPTCHA or progressive challenges in applications interacting with Synapse's Client API.
  • List of Threats Mitigated:
    • Brute-Force Login Attacks (High): Prevents attackers from rapidly trying passwords against user accounts on your Synapse instance.
    • Client-Side DoS/DDoS (High): Prevents malicious clients from overwhelming your Synapse server with API requests.
    • Account Enumeration (Medium): Makes it harder to enumerate valid usernames on your Synapse instance.
    • API Abuse (Medium): Limits the impact of malicious clients abusing Synapse API endpoints.
  • Impact:
    • Brute-Force Login Attacks (High): Significantly reduces the effectiveness of brute-force attacks against Synapse users.
    • Client-Side DoS/DDoS (High): Significantly reduces the impact of client-side DoS/DDoS attacks on Synapse.
    • Account Enumeration (Medium): Moderately reduces account enumeration risk on Synapse.
    • API Abuse (Medium): Moderately reduces API abuse targeting Synapse.
  • Currently Implemented:
    • Partially Implemented: Synapse has built-in client API rate limiting configurable directly in homeserver.yaml.
    • Location: Configuration is primarily in homeserver.yaml within the client_api section of your Synapse instance.
  • Missing Implementation:
    • Dynamic Rate Limiting based on Threat Intelligence within Synapse: Lack of integration within Synapse with threat intelligence feeds for dynamic rate limit adjustments.
    • User-Specific Rate Limiting Tiers within Synapse: Lack of ability within Synapse to implement different rate limiting tiers for different user groups.
    • Advanced CAPTCHA/Challenge Integration within Synapse Core: While CAPTCHA can be integrated externally, more sophisticated challenge mechanisms within Synapse core could be beneficial.

Mitigation Strategy: Restrict Access to the Admin API

5. Restrict Access to the Admin API

  • Mitigation Strategy: Admin API Access Control (Synapse Configuration)
  • Description:
    1. Configure admin_api_bind_address in homeserver.yaml: In homeserver.yaml, set admin_api_bind_address to 127.0.0.1 or an internal network interface to restrict Admin API access to localhost or internal networks for your Synapse instance.
    2. Use Access Tokens for Authentication (Synapse Feature): Admin API access to Synapse should be authenticated using access tokens, a built-in Synapse feature.
    3. Implement Network-Level Access Control (External to Synapse): Use firewall rules (external to Synapse itself) to further restrict access to the Admin API port.
    4. Regularly Rotate Admin API Access Tokens (Synapse Best Practice): Implement a policy for regularly rotating Synapse Admin API access tokens.
    5. Audit Admin API Access (Synapse Logging): Enable logging and auditing of Admin API requests within Synapse to monitor for unauthorized access.
  • List of Threats Mitigated:
    • Unauthorized Admin Access (High): Prevents unauthorized individuals from gaining administrative control over your Synapse instance via the Admin API.
    • Admin API Exploitation (High): Reduces the risk of attackers exploiting vulnerabilities in the Synapse Admin API.
    • Privilege Escalation (High): Prevents attackers from escalating privileges by gaining access to Synapse admin functionalities.
  • Impact:
    • Unauthorized Admin Access (High): Significantly reduces the risk of unauthorized admin access to Synapse.
    • Admin API Exploitation (High): Significantly reduces the risk of Synapse Admin API exploitation.
    • Privilege Escalation (High): Significantly reduces the risk of privilege escalation within Synapse.
  • Currently Implemented:
    • Partially Implemented: Synapse allows configuring admin_api_bind_address in homeserver.yaml and uses access tokens for Admin API authentication.
    • Location: Configuration in homeserver.yaml. Access token management is part of Synapse's admin functionalities.
  • Missing Implementation:
    • Role-Based Access Control (RBAC) for Admin API within Synapse: Synapse's Admin API access control is basic. RBAC within Synapse would allow for more granular permission management.
    • Multi-Factor Authentication (MFA) for Admin API within Synapse: Adding MFA directly to Synapse Admin API access would enhance security.
    • Automated Access Token Rotation within Synapse: Lack of built-in automated access token rotation mechanisms within Synapse itself.

Mitigation Strategy: Carefully Vet and Audit Modules

6. Carefully Vet and Audit Modules

  • Mitigation Strategy: Module Vetting and Auditing (Synapse Module Management)
  • Description:
    1. Source Code Review: Before installing any third-party Synapse module, review its source code.
    2. Dependency Analysis: Analyze the module's dependencies for vulnerabilities relevant to Synapse.
    3. Permissions Review: Understand the permissions the module requests within Synapse and ensure least privilege.
    4. Community Reputation Check: Research the module's developer and community reputation in the context of Synapse modules.
    5. Security Testing: If possible, perform security testing on the module in a test Synapse environment.
    6. Regular Audits: Periodically re-audit installed Synapse modules.
  • List of Threats Mitigated:
    • Malicious Module Installation (High): Prevents installing intentionally malicious Synapse modules.
    • Vulnerable Module Installation (Medium - High): Reduces the risk of installing Synapse modules with vulnerabilities.
    • Accidental Misconfiguration by Modules (Medium): Minimizes risk of modules unintentionally misconfiguring Synapse.
  • Impact:
    • Malicious Module Installation (High): Significantly reduces the risk of malicious Synapse module installation.
    • Vulnerable Module Installation (High): Significantly reduces the risk of vulnerable Synapse module installation.
    • Accidental Misconfiguration by Modules (Medium): Moderately reduces misconfiguration risks related to Synapse modules.
  • Currently Implemented:
    • Not Implemented by Default in Synapse: This is a manual process external to Synapse's core functionality. Synapse doesn't enforce module vetting.
    • Location: This is an organizational process, not directly implemented within Synapse software itself.
  • Missing Implementation:
    • Automated Module Security Scanning for Synapse Modules: Lack of automated tools integrated with Synapse to scan modules for vulnerabilities before installation.
    • Module Sandboxing/Isolation within Synapse: Synapse modules currently have broad access. Sandboxing within Synapse would limit the impact of compromised modules.
    • Centralized Module Registry with Security Ratings for Synapse Modules: Lack of a centralized registry for Synapse modules with security ratings or vulnerability information.