threat-modeling.md

Threat Model Analysis for openresty/lua-nginx-module

Threat: Lua Injection

Description: An attacker injects malicious Lua code by manipulating user-supplied input that is not properly sanitized and is used to construct Lua code dynamically. The attacker can execute arbitrary Lua code on the server within the Nginx worker process, potentially gaining full control of the application and server. * Impact: Critical. Full server compromise, data breach, data manipulation, denial of service, and further attacks on internal networks. * Affected Component: Lua scripts, lua-nginx-module core module. * Risk Severity: Critical * Mitigation Strategies: * Avoid dynamic Lua code generation based on user input. * Use parameterized queries for database interactions. * Sanitize and validate all user inputs before using them in Lua logic. * Implement input validation at multiple layers (client-side and server-side).

Threat: Vulnerable Lua Libraries

Description: An attacker exploits known vulnerabilities in outdated or insecure Lua libraries used by the application through lua-nginx-module. This can be achieved by sending crafted requests that trigger the vulnerability in the library, leading to various outcomes like remote code execution, denial of service, or information disclosure. * Impact: High to Critical (depending on the vulnerability). Remote code execution, data breach, denial of service, information disclosure. * Affected Component: Lua scripts, external Lua libraries (e.g., JSON parsers, XML parsers, database drivers) used with lua-nginx-module. * Risk Severity: High * Mitigation Strategies: * Maintain an inventory of all Lua libraries and dependencies used. * Regularly update Lua libraries to the latest stable versions. * Subscribe to security advisories for used Lua libraries. * Perform security audits and vulnerability scanning of Lua libraries.

Threat: Lua Denial of Service (DoS)

Description: An attacker crafts requests that cause Lua code executed by lua-nginx-module to consume excessive server resources (CPU, memory, I/O). This can be achieved by triggering computationally intensive Lua operations, infinite loops, or blocking I/O without timeouts, leading to application slowdown or complete denial of service. * Impact: High. Denial of service, application unavailability, resource exhaustion. * Affected Component: Lua scripts, ngx.timer, ngx.sleep, ngx.socket (if used improperly), lua-nginx-module core module. * Risk Severity: High * Mitigation Strategies: * Implement resource limits and timeouts in Lua code, especially for loops and external operations. * Profile Lua code for performance bottlenecks and optimize resource-intensive sections. * Use non-blocking APIs provided by lua-nginx-module where possible. * Monitor resource usage of Nginx worker processes and set up alerts for unusual spikes.

Threat: Access Control Bypass through Lua Logic

Description: An attacker bypasses intended access control mechanisms by exploiting flaws in custom access control logic implemented in Lua within lua-nginx-module. This can occur if Lua code incorrectly validates user roles, permissions, or authentication tokens, allowing unauthorized access to protected resources or functionalities. * Impact: High. Unauthorized access to sensitive data and functionalities, data manipulation, privilege escalation. * Affected Component: Lua scripts, custom authentication/authorization logic within lua-nginx-module. * Risk Severity: High * Mitigation Strategies: * Carefully design and test access control logic in Lua. * Leverage Nginx's built-in access control modules where possible. * Ensure Lua code correctly integrates with and enforces existing access control policies.

Threat: Insecure Upstream Proxying via Lua

Description: An attacker intercepts or manipulates communication between the Nginx server and upstream servers when Lua code (using lua-nginx-module features like ngx.location.capture or ngx.proxy_pass) is used for proxying requests. This can occur if insecure protocols (HTTP instead of HTTPS) are used, TLS verification is disabled, or input to upstream requests is not properly sanitized, leading to man-in-the-middle attacks, data breaches, or injection vulnerabilities in upstream systems. * Impact: High. Data breach, man-in-the-middle attacks, compromise of upstream systems. * Affected Component: Lua scripts, ngx.location.capture, ngx.proxy_pass, ngx.socket.tcp from lua-nginx-module. * Risk Severity: High * Mitigation Strategies: * Always use HTTPS for upstream connections when handling sensitive data. * Implement proper TLS verification for upstream connections to prevent man-in-the-middle attacks. * Sanitize and validate data passed to upstream servers to prevent injection vulnerabilities in upstream systems.

Threat: Lua Blocking Operations DoS

Description: An attacker triggers blocking operations in Lua code executed by lua-nginx-module (e.g., synchronous file I/O, blocking network requests) by sending specific requests. This can block Nginx worker processes, leading to performance degradation and denial of service for legitimate users. * Impact: High. Denial of service, application unavailability, performance degradation. * Affected Component: Lua scripts, synchronous I/O operations within Lua (avoid these when using lua-nginx-module). * Risk Severity: High * Mitigation Strategies: * Strictly avoid blocking operations in Lua code within Nginx context. * Use non-blocking APIs provided by lua-nginx-module (e.g., ngx.timer, ngx.socket with timeouts). * Offload blocking tasks to external services or background processes.

Threat: CPU Intensive Lua Code DoS

Description: An attacker sends requests designed to trigger CPU-intensive Lua code execution within lua-nginx-module. This can exhaust server CPU resources, leading to performance degradation and denial of service for other users. Examples include complex regular expression matching, cryptographic operations without proper limits, or inefficient algorithms in Lua code. * Impact: High. Denial of service, application unavailability, performance degradation. * Affected Component: Lua scripts, CPU-intensive Lua functions or operations within lua-nginx-module. * Risk Severity: High * Mitigation Strategies: * Optimize Lua code for performance and avoid unnecessary CPU-intensive operations. * Cache results of CPU-intensive computations where appropriate. * Profile Lua code for CPU usage and identify performance bottlenecks. * Implement rate limiting and request throttling to mitigate abusive requests targeting CPU-intensive endpoints.

Threat: Insecure Lua Module Loading

Description: An attacker gains the ability to load malicious Lua modules into the application by exploiting insecure configurations of lua_package_path or lua_package_cpath in Nginx, which are used by lua-nginx-module. This could allow the attacker to execute arbitrary code within the Nginx worker process by placing or modifying Lua modules in accessible paths. * Impact: Critical. Remote code execution, full server compromise, data breach, data manipulation. * Affected Component: Nginx configuration, lua_package_path, lua_package_cpath directives (used by lua-nginx-module), Lua module loading mechanism. * Risk Severity: Critical * Mitigation Strategies: * Restrict lua_package_path and lua_package_cpath to trusted and necessary locations only. * Ensure that directories specified in lua_package_path and lua_package_cpath are not world-writable and have appropriate access permissions. * Use code signing or checksums to verify the integrity of Lua modules before loading them.