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attack-surface.md

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Attack Surface Analysis for evanw/esbuild

Attack Surface: Insecure define Replacements

  • Description: Substitution of global identifiers with constant expressions, potentially exposing sensitive data.
  • esbuild Contribution: esbuild's define feature provides the mechanism for this substitution. This is a direct feature of esbuild.
  • Example: 
    // esbuild config
{
  define: {
    'process.env.SECRET_API_KEY': '"YOUR_ACTUAL_API_KEY"' // INSECURE!
  }
}
    This embeds the API key directly into the bundled JavaScript.
  • Impact: Information Disclosure (API keys, secrets, internal feature flags), Potential Privilege Escalation.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Never hardcode secrets in define.
    • Use environment variables loaded securely at runtime. define should only reference the variable name, not its value: define: { 'process.env.API_KEY': 'process.env.API_KEY' }.
    • Employ a secrets management solution (e.g., HashiCorp Vault, AWS Secrets Manager, Azure Key Vault).
    • Implement code reviews and automated static analysis to detect hardcoded secrets.

Attack Surface: Malicious or Vulnerable Plugins

  • Description: Third-party esbuild plugins that contain malicious code or known vulnerabilities.
  • esbuild Contribution: esbuild's plugin API allows for extensibility, but also introduces a vector for untrusted code. This is a direct feature of esbuild.
  • Example: A plugin claiming to optimize images but actually exfiltrates build artifacts or injects a backdoor. Or, a legitimate plugin with a known vulnerability in one of its dependencies.
  • Impact: Code Injection, Supply Chain Attack, Data Exfiltration, Denial of Service.
  • Risk Severity: High
  • Mitigation Strategies:
    • Use only plugins from trusted, reputable sources.
    • Thoroughly vet plugin source code before use.
    • Pin plugin versions to specific, audited releases.
    • Regularly update plugins and their dependencies to patch vulnerabilities.
    • Use Software Composition Analysis (SCA) tools to identify vulnerable dependencies.
    • Implement a strict plugin approval process.

Attack Surface: Misconfigured external Dependencies

  • Description: Incorrectly marking modules as external, leading to runtime loading from potentially untrusted sources.
  • esbuild Contribution: The external option in esbuild's configuration controls which modules are bundled. This is a direct feature of esbuild.
  • Example: 
    // esbuild config
{
  external: ['my-internal-security-module'] // Incorrect!
}
    If my-internal-security-module is not a truly external dependency (e.g., a Node.js built-in), it might be loaded from an attacker-controlled location at runtime.
  • Impact: Code Injection, Supply Chain Attack.
  • Risk Severity: High
  • Mitigation Strategies:
    • Carefully review and validate the external configuration. Ensure only truly external dependencies are listed.
    • Use a lockfile (package-lock.json, yarn.lock) for consistent dependency resolution.
    • If loading external modules at runtime, use a CDN with Subresource Integrity (SRI) where possible.

Attack Surface: Loader Misconfiguration or Vulnerable Custom Loaders

  • Description: Incorrectly configured loaders or the use of custom loaders with security flaws.
  • esbuild Contribution: esbuild's loader system determines how different file types are processed. This is a direct feature of esbuild.
  • Example: A custom loader designed to handle a specific file format but contains a vulnerability that allows an attacker to inject arbitrary code when processing a maliciously crafted file. Or, misconfiguring the text loader to execute arbitrary code embedded within a text file.
  • Impact: Code Injection, Data Exfiltration, Denial of Service.
  • Risk Severity: High
  • Mitigation Strategies:
    • Thoroughly review and validate loader configurations.
    • Avoid using custom loaders from untrusted sources.
    • If using custom loaders, rigorously audit their code for security vulnerabilities.
    • Ensure loaders are correctly configured for the intended file types.
    • Regularly update loaders to their latest versions.