attack-surface.md

Attack Surface Analysis for nodejs/string_decoder

Attack Surface: Encoding Mismatches and Encoding Confusion

• Description: The encoding used by string_decoder does not match the actual encoding of the input Buffer, or an attacker can manipulate the encoding parameter used when initializing string_decoder. This leads to incorrect decoding.
• string_decoder Contribution: string_decoder's core functionality is encoding and decoding. Providing an incorrect or attacker-controlled encoding directly subverts its intended operation, leading to misinterpretation of data.
• Example: An application expects UTF-8 encoded usernames. Due to a vulnerability, an attacker can influence the encoding parameter used to initialize string_decoder to 'latin1'. When the attacker submits a UTF-8 username containing characters that have different representations in Latin-1, string_decoder incorrectly decodes it. This could bypass input validation checks that rely on UTF-8 character properties or lead to stored data being misinterpreted later.
• Impact: Incorrect data interpretation, security bypasses if encoding confusion leads to misinterpretation of security-sensitive data (e.g., authentication credentials, authorization rules), potential for injection attacks if attacker controls encoding and content, leading to execution of unintended commands or scripts due to misparsed input.
• Risk Severity: High
• Mitigation Strategies:
  • Explicit Encoding Definition: Statically define and enforce the expected encoding for string_decoder within the application code. Avoid relying on external configuration or user-provided encoding parameters unless absolutely necessary and rigorously validated.
  • Encoding Validation: If the encoding must be derived from external sources (which is generally discouraged for security reasons), strictly validate it against a very limited whitelist of explicitly allowed and safe encodings. Reject any encoding that is not on the whitelist.
  • Consistent Encoding Handling: Maintain consistent encoding handling throughout the entire application lifecycle, from data input and processing to storage and output. Ensure that all components interacting with string data operate under the same encoding assumptions to prevent mismatches when using string_decoder.
  • Output Sanitization and Contextual Encoding Awareness: Sanitize and validate the decoded string after using string_decoder, especially if it is used in security-sensitive operations, displayed to users, or used to construct further commands or queries. Be aware of the encoding context in which the decoded string will be used to prevent injection vulnerabilities.