attack-surface.md

Attack Surface Analysis for elixir-lang/elixir

Attack Surface: Process Exhaustion (DoS)

• Description: An attacker overwhelms the application by triggering the creation of an excessive number of Elixir processes, exceeding system resource limits and causing a Denial of Service.
• Elixir Contribution: Elixir's lightweight process model, while a core strength, becomes a vulnerability if process creation is unbounded. The ease of spawning processes can be exploited to rapidly consume resources.
• Example: An endpoint designed to handle user uploads spawns a new Elixir process per upload request. A malicious user floods this endpoint with numerous upload requests, quickly exhausting available processes and crashing the application.
• Impact: Denial of Service, application unavailability, system crash.
• Risk Severity: High
• Mitigation Strategies:
  • Implement Rate Limiting: Limit the number of requests from a single IP or user within a timeframe.
  • Use Backpressure and Queueing: Employ mechanisms like GenStage or message queues to control the rate of process creation and handle bursts of requests gracefully.
  • Set Process Limits: Configure the Erlang VM to limit the maximum number of processes allowed.
  • Resource Monitoring and Auto-Scaling: Monitor system resources and implement auto-scaling to handle increased load.

Attack Surface: Code Injection via Code.eval_string

• Description: An attacker injects and executes arbitrary Elixir code by manipulating input that is processed by functions like Code.eval_string or similar dynamic code execution features.
• Elixir Contribution: Elixir's Code.eval_string function is designed for dynamic code evaluation. Its direct use with unsanitized user input creates a critical code injection vulnerability, a direct consequence of Elixir's dynamic capabilities.
• Example: An application uses Code.eval_string to dynamically generate and execute Elixir code based on user-provided configuration. A malicious user injects Elixir code within this configuration, leading to arbitrary code execution on the server.
• Impact: Remote Code Execution, full system compromise, data breach, complete application takeover.
• Risk Severity: Critical
• Mitigation Strategies:
  • Absolutely Avoid Code.eval_string with User Input: Never use Code.eval_string or similar functions to process user-controlled input. Dynamic code execution from external sources should be eliminated.
  • Use Alternative, Safe Approaches: Refactor code to avoid dynamic code generation based on user input. Use data-driven approaches, configuration files, or predefined logic instead.
  • If Absolutely Necessary (Extreme Caution): If dynamic code execution is unavoidable, implement extremely rigorous input validation and sanitization, using whitelisting and sandboxing techniques (though sandboxing in Elixir/Erlang is complex and not a primary security feature).

Attack Surface: Command Injection via System.cmd

• Description: An attacker injects and executes arbitrary system commands by manipulating input that is passed to Elixir functions like System.cmd or Port.open, leading to shell command execution.
• Elixir Contribution: Elixir's System.cmd function provides direct access to system shell commands. Unsafe use of this function with user-provided input directly enables command injection vulnerabilities within Elixir applications.
• Example: An application uses System.cmd to process files based on user-provided filenames. A malicious user injects shell commands into the filename, which are then executed by System.cmd, potentially compromising the server.
• Impact: Remote Command Execution, system compromise, data exfiltration, denial of service, privilege escalation.
• Risk Severity: Critical
• Mitigation Strategies:
  • Avoid System.cmd with User Input: Do not use System.cmd or related functions to execute commands based on any user-provided data.
  • Use Libraries or Built-in Functions: Prefer using Elixir libraries or Erlang modules that provide the necessary functionality without resorting to external shell commands.
  • Strict Input Validation and Sanitization (If Unavoidable): If System.cmd with user input is absolutely necessary, implement extremely strict input validation, sanitization, and command parameterization to prevent injection. Use whitelisting and escape shell metacharacters.
  • Principle of Least Privilege: Run the application with minimal necessary system privileges to limit the impact of command injection.

Attack Surface: Erlang Distribution Protocol Vulnerabilities

• Description: Exploitation of security vulnerabilities within the Erlang Distribution Protocol, used for clustering Elixir/Erlang nodes, leading to unauthorized access, remote code execution, or information disclosure within the cluster.
• Elixir Contribution: Elixir applications leveraging Erlang distribution for clustering inherit the security risks associated with the Erlang Distribution Protocol. Vulnerabilities in this protocol directly impact the security of clustered Elixir applications.
• Example: Historical vulnerabilities in the Erlang Distribution Protocol allowed attackers to bypass authentication by exploiting weaknesses in the Erlang cookie mechanism. Successful exploitation could grant an attacker remote shell access to nodes in the cluster.
• Impact: Remote Code Execution, cluster-wide compromise, lateral movement, data breaches, denial of service across the cluster.
• Risk Severity: High to Critical
• Mitigation Strategies:
  • Strong Erlang Cookie Management: Generate and securely manage strong, unpredictable Erlang cookies. Protect cookie files from unauthorized access.
  • Network Segmentation and Firewalls: Isolate Erlang distribution ports (4369 and ephemeral ports) using firewalls to restrict communication to trusted nodes within a secure network segment.
  • Disable Distribution if Unnecessary: If clustering via Erlang distribution is not required, disable it entirely to eliminate this attack surface.
  • Regular Erlang/OTP Updates: Keep Erlang/OTP updated to the latest versions to patch known vulnerabilities in the distribution protocol and benefit from security improvements.
  • Consider Secure Distribution Alternatives (if available): Explore and utilize more secure distribution mechanisms offered in newer Erlang/OTP versions if they become available.

Attack Surface: Plug Vulnerabilities (Custom Plugs in Phoenix)

• Description: Security vulnerabilities introduced in custom Plugs within Phoenix applications, particularly in authentication, authorization, or input validation logic, leading to bypasses or other security flaws.
• Elixir Contribution: Phoenix framework's request pipeline relies on Plugs, which are Elixir modules. Vulnerabilities in custom-written Plugs, a core component of Phoenix/Elixir web applications, directly expose the application to security risks.
• Example: A custom authentication Plug in a Phoenix application contains a logic flaw that allows users to bypass authentication by manipulating request headers or cookies. This grants unauthorized access to protected resources.
• Impact: Authentication bypass, authorization bypass, access control failures, information disclosure, privilege escalation.
• Risk Severity: High to Critical
• Mitigation Strategies:
  • Secure Plug Development Practices: Follow secure coding principles when developing custom Plugs, especially for security-critical functions like authentication and authorization.
  • Thorough Plug Testing and Code Reviews: Implement comprehensive unit and integration tests for Plugs, and conduct regular code reviews to identify potential security vulnerabilities.
  • Leverage Established Security Libraries: Utilize well-vetted Elixir libraries for authentication and authorization (e.g., Pow, Guardian) instead of creating custom security logic from scratch.
  • Principle of Least Privilege in Plugs: Design Plugs to operate with the minimum necessary permissions and avoid overly complex security logic.

Attack Surface: Insecure NIFs (Native Implemented Functions)

• Description: Security vulnerabilities within Native Implemented Functions (NIFs), which are Elixir/Erlang functions written in C or other native languages, leading to memory corruption, crashes, or arbitrary code execution in the Erlang VM.
• Elixir Contribution: Elixir's NIF mechanism allows integration with native code for performance-critical tasks. However, vulnerabilities in NIFs, due to memory safety issues in native languages, can directly compromise the Elixir application and the Erlang VM itself.
• Example: A NIF written in C has a buffer overflow vulnerability. When called from Elixir with maliciously crafted input, this overflow corrupts memory within the Erlang VM, potentially leading to crashes or remote code execution.
• Impact: Remote Code Execution, Erlang VM crash, system instability, complete application compromise.
• Risk Severity: Critical
• Mitigation Strategies:
  • Minimize NIF Usage: Avoid using NIFs unless absolutely necessary for performance reasons. Explore Elixir/Erlang solutions first.
  • Secure NIF Development Practices: If NIFs are required, follow extremely rigorous secure coding practices in the native code (C, Rust, etc.). Pay close attention to memory management, input validation, and buffer handling to prevent vulnerabilities like buffer overflows, use-after-free, etc.
  • Thorough NIF Testing and Auditing: Conduct extensive testing and security audits of NIF code, including static and dynamic analysis, to identify and eliminate potential vulnerabilities. Use memory safety tools during development.
  • Sandboxing and Isolation (Limited): Explore any available sandboxing or isolation mechanisms for NIFs within the Erlang/OTP environment, although full sandboxing of NIFs is complex.

Attack Surface: Deserialization Vulnerabilities (Potentially via Erlang Term Format - ETF)

• Description: Exploitation of vulnerabilities during the deserialization of data, particularly when using Erlang Term Format (ETF), potentially leading to code execution or other security issues.
• Elixir Contribution: Elixir and Erlang commonly use ETF for inter-node communication and data serialization. If deserialization of ETF data is not handled securely, vulnerabilities can arise, especially if untrusted or attacker-controlled ETF data is processed.
• Example: A vulnerability in an ETF deserialization library or custom deserialization logic could be exploited by crafting malicious ETF data. When the Elixir application deserializes this data, it could trigger code execution or other unintended behavior.
• Impact: Remote Code Execution, data corruption, denial of service, application compromise.
• Risk Severity: High
• Mitigation Strategies:
  • Careful ETF Deserialization: Exercise caution when deserializing ETF data, especially if it originates from untrusted sources.
  • Use Well-Vetted Deserialization Libraries: Rely on established and well-maintained libraries for ETF deserialization. Avoid implementing custom deserialization logic if possible.
  • Input Validation and Sanitization (Pre-Deserialization): If possible, validate and sanitize data before deserialization to detect and reject potentially malicious payloads.
  • Regular Updates of Dependencies: Keep ETF-related libraries and Erlang/OTP updated to benefit from security patches and improvements in deserialization handling.
  • Consider Alternative Serialization Formats (If Applicable): If ETF is not strictly required, consider using alternative serialization formats that might have a smaller attack surface or better security properties for specific use cases.

Attack Surface: LiveView State Manipulation

• Description: Attackers manipulate client-side state or WebSocket messages in Phoenix LiveView applications to bypass security checks or achieve unintended actions by exploiting insufficient server-side validation of state transitions.
• Elixir Contribution: Phoenix LiveView, built with Elixir, introduces stateful client-server communication via WebSockets. If server-side validation of LiveView state and incoming events is inadequate, attackers can exploit this Elixir-specific framework feature to manipulate application behavior.
• Example: A LiveView application manages user roles in its state. If the server-side event handlers don't properly validate state update messages from the client, an attacker could craft WebSocket messages to elevate their own role in the LiveView state, bypassing authorization checks.
• Impact: Authorization bypass, privilege escalation, data manipulation, unexpected application behavior, potential for further exploitation depending on the manipulated state.
• Risk Severity: High
• Mitigation Strategies:
  • Strict Server-Side State Validation: Always perform rigorous validation of all state transitions and incoming events on the server-side within LiveView event handlers. Never rely on client-side validation for security.
  • Input Sanitization in LiveView Handlers: Sanitize and validate all user input received through LiveView events before processing it or updating state.
  • Authorization Checks in LiveView Handlers: Implement authorization checks within LiveView event handlers to ensure users are permitted to perform actions based on the current state and incoming messages.
  • Stateless Design Principles (where feasible): Design LiveView components to be as stateless as possible to minimize the attack surface related to state manipulation.
  • Secure WebSocket Communication (WSS): Ensure WebSocket communication is encrypted using WSS to protect against eavesdropping and message tampering.