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attack-surface.md

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Attack Surface Analysis for evanw/esbuild

Attack Surface: Malicious Code Injection via Input Files

  • Description: Vulnerabilities in esbuild's parsers (JavaScript, TypeScript, CSS, etc.) could allow attackers to inject malicious code by crafting specially crafted input files.
  • esbuild Contribution: esbuild's core functionality relies on parsing and processing various file types. Bugs in these parsers directly create this attack surface.
  • Example: An attacker crafts a malicious JavaScript file that exploits a buffer overflow vulnerability in esbuild's JavaScript parser. When esbuild processes this file during the build, it executes arbitrary code on the build server.
  • Impact:
    • Code execution on the build server.
    • Data exfiltration from the build environment.
    • Compromise of the build pipeline and potentially deployed application.
    • Denial of Service of the build process.
  • Risk Severity: High to Critical
  • Mitigation Strategies:
    • Keep esbuild Updated: Regularly update esbuild to the latest version to benefit from parser bug fixes and security patches.
    • Input Sanitization (if applicable): If any part of the build process involves processing user-provided content that ends up as input to esbuild, sanitize or validate this input.
    • Secure Build Environment: Isolate the build environment to limit the impact of potential code execution. Use containerization and least privilege principles.

Attack Surface: Path Traversal via Input Paths

  • Description: Improper handling of file paths by esbuild or its plugins could allow attackers to access files outside the intended project directory during the build process using path traversal techniques.
  • esbuild Contribution: esbuild works with file paths to locate input files, dependencies, and output directories. Incorrect path handling in esbuild or plugins can lead to this vulnerability.
  • Example: A plugin used with esbuild incorrectly handles a user-provided configuration option that includes a file path. An attacker manipulates this configuration to include a path like ../../sensitive/config.json, causing the plugin (and potentially esbuild) to read and expose this sensitive file during the build.
  • Impact:
    • Information disclosure of sensitive files on the build server.
    • Potential for further exploitation if exposed files contain credentials or configuration details.
  • Risk Severity: Medium to High (can escalate to high depending on the sensitivity of accessible files).
  • Mitigation Strategies:
    • Carefully Review Plugin Code and Configurations: Thoroughly examine the code and configurations of any esbuild plugins, especially those that handle file paths.
    • Restrict File System Access: Configure esbuild and plugins to operate within a restricted file system scope. Use configuration options or operating system-level permissions to limit access.
    • Input Validation and Sanitization for Paths (in Plugins): If developing plugins, rigorously validate and sanitize any file paths received as input to prevent traversal attacks.

Attack Surface: Malicious or Vulnerable Plugins

  • Description: Using third-party esbuild plugins introduces the risk of supply chain attacks or vulnerabilities within the plugin code itself.
  • esbuild Contribution: esbuild's plugin architecture encourages extending its functionality with external code, inherently creating a dependency on plugin security.
  • Example: A popular but compromised esbuild plugin is used in a project. This plugin contains malicious code that exfiltrates environment variables from the build server to an attacker-controlled server during the build process.
  • Impact:
    • Supply chain compromise leading to code execution on the build server.
    • Data exfiltration.
    • Compromise of the build pipeline.
    • Vulnerabilities introduced into the built application if the plugin affects the output code.
  • Risk Severity: Medium to High (can escalate to high depending on plugin permissions and impact).
  • Mitigation Strategies:
    • Plugin Vetting and Auditing: Carefully vet and audit all third-party plugins before use. Check plugin reputation, maintainer activity, and code quality.
    • Dependency Scanning for Plugins: Use dependency scanning tools to check plugins and their dependencies for known vulnerabilities.
    • Principle of Least Privilege for Plugins: Configure plugins with the minimum necessary permissions and access. Avoid plugins that request excessive permissions.
    • Consider Plugin Alternatives or Custom Implementations: Evaluate if plugin functionality can be achieved through built-in esbuild features or by developing a custom, in-house plugin with stricter security controls.