threat-modeling.md

Threat Model Analysis for apache/solr

Threat: Unauthenticated Admin UI/API Access

• Description: An attacker directly accesses the Solr Admin UI or API endpoints (e.g., /solr/admin/, /solr/<collection>/select) without providing any credentials. The attacker can then issue arbitrary commands, view data, modify configurations, or even shut down the Solr instance.
• Impact:
  • Complete data breach (read all indexed data).
  • Data modification or deletion.
  • Service disruption (DoS, shutdown).
  • System compromise (if RCE vulnerabilities exist).
• Affected Solr Component:
  • Solr Admin UI (web interface).
  • Solr API endpoints (all request handlers).
  • Authentication and Authorization plugins (if misconfigured or disabled).
• Risk Severity: Critical
• Mitigation Strategies:
  • Enable Authentication: Implement Solr's built-in authentication (Basic Auth, Kerberos, etc.) using the security.json file. Use strong, unique passwords.
  • Network Segmentation: Restrict network access to the Solr Admin UI and API to a trusted internal network using firewall rules (e.g., iptables, AWS Security Groups). Do not expose Solr directly to the public internet.
  • IP Whitelisting: Configure Solr to only accept connections from specific, trusted IP addresses or ranges.
  • Disable Admin UI (if possible): If the Admin UI is not strictly required for operational tasks, disable it entirely via configuration.
  • Use a Reverse Proxy: Place a reverse proxy (e.g., Nginx, Apache) in front of Solr to handle authentication and authorization before requests reach Solr.

Threat: Information Disclosure via Query Parameters

• Description: An attacker crafts malicious queries using specific Solr query parameters to reveal sensitive information. Examples:
  • fl=*: Returns all fields, potentially exposing internal or sensitive data.
  • debugQuery=on: Reveals detailed query parsing and scoring information, including field names and internal structures.
  • facet.field=<sensitive_field>: Enumerates all values of a sensitive field, even if the user doesn't have direct access to read that field's data.
  • Using terms component to enumerate field values.
• Impact:
  • Leakage of sensitive data (PII, internal IDs, etc.).
  • Exposure of index structure and internal field names.
  • Facilitates further attacks (e.g., crafting more targeted queries).
• Affected Solr Component:
  • Query Parsers (e.g., Standard, DisMax, eDisMax).
  • Request Handlers (e.g., /select, /query).
  • Faceting components.
  • Terms component.
• Risk Severity: High
• Mitigation Strategies:
  • Input Validation and Sanitization: Strictly validate and sanitize all user-supplied input used in Solr queries. Use a whitelist approach for allowed parameters and values.
  • Parameter Whitelisting: Implement a strict whitelist of allowed query parameters and their permitted values. Reject any requests containing unauthorized parameters.
  • Field List Control (fl): Never use fl=* in production. Explicitly specify the required fields in the fl parameter.
  • Disable Debugging (debugQuery): Ensure debugQuery=on (and similar debugging options) is disabled in production environments.
  • Facet Restrictions: Limit faceting to specific, non-sensitive fields. Control the number of facet values returned (facet.limit). Consider using the JSON Facet API for more granular control.
  • Request Handler Configuration: Configure request handlers to restrict the use of potentially dangerous parameters.

Threat: Denial of Service via Expensive Queries

• Description: An attacker submits computationally expensive queries designed to consume excessive server resources (CPU, memory, disk I/O). Examples:
  • Queries with leading wildcards (e.g., *sensitive).
  • Complex regular expressions.
  • Deeply nested boolean queries.
  • Queries with very large rows values.
  • Excessive faceting requests.
  • Joins or graph queries on large datasets.
• Impact:
  • Solr server becomes unresponsive.
  • Legitimate users are unable to access the service.
  • Potential for cascading failures if Solr is a critical component.
• Affected Solr Component:
  • Query Parsers.
  • Request Handlers.
  • Caching mechanisms (if overwhelmed).
  • Underlying JVM and operating system.
• Risk Severity: High
• Mitigation Strategies:
  • Query Timeouts: Set reasonable timeouts for Solr queries (e.g., using timeAllowed parameter) to prevent long-running queries from consuming resources indefinitely.
  • Resource Limits: Configure Solr and the underlying JVM to limit the resources (CPU, memory) that can be consumed by a single query or request.
  • Disable/Restrict Expensive Query Types: If leading wildcard queries, complex regular expressions, or other expensive query types are not essential, disable them or restrict their use to trusted users/roles.
  • Rate Limiting: Implement rate limiting (at the application or network level) to prevent attackers from submitting a large number of requests in a short period.
  • Caching: Use Solr's caching mechanisms effectively to reduce the load on the server. However, ensure the cache itself is not vulnerable to DoS.
  • Monitoring: Continuously monitor Solr's resource usage (CPU, memory, disk I/O, query latency) to detect and respond to potential DoS attacks.

Threat: Remote Code Execution (RCE) via VelocityResponseWriter

• Description: An attacker exploits a vulnerability in older versions of Solr's VelocityResponseWriter to execute arbitrary code on the Solr server. This typically involves injecting malicious Velocity template code.
• Impact:
  • Complete system compromise.
  • Data theft, modification, or deletion.
  • Installation of malware.
  • Use of the compromised server for further attacks.
• Affected Solr Component:
  • VelocityResponseWriter (specifically, older, vulnerable versions).
• Risk Severity: Critical
• Mitigation Strategies:
  • Upgrade Solr: This is the primary and most effective mitigation. Upgrade to a recent, patched version of Solr where this vulnerability has been addressed.
  • Disable VelocityResponseWriter: If upgrading is not immediately possible, disable the VelocityResponseWriter entirely if it is not absolutely required for your application. This can be done in solrconfig.xml.
  • Input Validation (if VelocityResponseWriter must be used): If you must use an older, vulnerable version and cannot disable the component, implement extremely rigorous input validation and sanitization to prevent the injection of malicious Velocity template code. This is a very risky approach and should be avoided if at all possible.

Threat: XML External Entity (XXE) Injection

• Description: An attacker submits a malicious XML document to a Solr endpoint that is configured to process XML. The XML contains external entity references that, when processed, can lead to:
  • Reading local files on the Solr server.
  • Accessing internal network resources.
  • Denial of service.
• Impact:
  • Information disclosure (local files, internal network data).
  • Denial of service.
  • Potential for server-side request forgery (SSRF).
• Affected Solr Component:
  • Any Solr component that processes XML input (e.g., Update handlers, DataImportHandler).
  • XML Query Parser.
• Risk Severity: High
• Mitigation Strategies:
  • Disable External Entities: Configure Solr's XML parser to disable the processing of external entities and DTDs. This is the most effective mitigation. This can often be done through JVM system properties (e.g., -Djavax.xml.accessExternalDTD="" -Djavax.xml.accessExternalSchema="") or within solrconfig.xml.
  • Use JSON: Prefer JSON over XML for data exchange with Solr. JSON parsers are generally less susceptible to XXE attacks.
  • Input Validation: If XML input is unavoidable, validate the XML against a strict schema before passing it to Solr.

Threat: Index Corruption/Deletion

• Description: An attacker with write access to the Solr index (either through compromised credentials or a misconfigured authorization system) intentionally corrupts or deletes the index data.
• Impact:
  • Data loss.
  • Service disruption.
  • Loss of search functionality.
• Affected Solr Component:
  • Update Handlers (e.g., /update, /update/json, /update/csv).
  • Solr Admin UI (if write access is granted).
• Risk Severity: High
• Mitigation Strategies:
  • Strict Authorization: Implement strict authorization rules using Solr's authorization framework. Limit write access to the index to only authorized users and roles. Use the principle of least privilege.
  • Regular Backups: Implement a robust backup and recovery strategy for the Solr index. Regularly back up the index data to a secure location. Test the restoration process.
  • Replication: Use Solr's replication feature to create redundant copies of the index. This provides high availability and fault tolerance, allowing you to quickly recover from index corruption or deletion.
  • Audit Logging: Enable detailed audit logging to track all write operations to the index. This can help identify the source of any malicious activity.

Threat: Misconfigured DataImportHandler (DIH)

• Description: An attacker exploits a misconfigured DataImportHandler to:
  • Upload malicious files to the Solr server.
  • Inject arbitrary data into the index.
  • Execute arbitrary code (if the DIH is configured to use scripting).
• Impact:
  • System compromise (if malicious files are executed).
  • Data corruption.
  • Information disclosure.
• Affected Solr Component:
  • DataImportHandler (DIH).
• Risk Severity: High
• Mitigation Strategies:
  • Secure DIH Configuration: Carefully review and secure the DIH configuration (data-config.xml).
  • Restrict File Access: If the DIH is used to import data from files, restrict the directories that Solr can access. Do not allow Solr to read files from arbitrary locations on the filesystem.
  • Disable Scripting (if possible): If scripting is not required, disable it in the DIH configuration. If scripting is necessary, use a secure scripting engine and carefully validate any user-supplied input.
  • Input Validation: Validate and sanitize all data imported through the DIH.
  • Authorization: Restrict access to the DIH to authorized users and roles.