attack-surface.md

Attack Surface Analysis for square/okio

Attack Surface: Unsafe Data Deserialization

• Description: Vulnerabilities arising from improper handling of data read by Okio's BufferedSource when the application attempts to deserialize or interpret it as structured data. Even though Okio deals with bytes, applications might parse binary formats or other structured data read through Okio.
• Okio Contribution: Okio's BufferedSource provides an efficient way to read byte streams, which can be the input for deserialization processes within the application. If the application doesn't validate data read via BufferedSource, it can be vulnerable.
• Example: An application reads binary data using Okio from a network source and attempts to deserialize it into application objects without proper validation. A malicious actor crafts a byte stream that, when deserialized, exploits a vulnerability in the application's deserialization logic, leading to code execution.
• Impact: Code execution, data corruption, information disclosure, denial of service.
• Risk Severity: High
• Mitigation Strategies:
  • Input Validation: Thoroughly validate all data read from BufferedSource before attempting to deserialize or interpret it.
  • Secure Deserialization Libraries: Use well-established and secure serialization libraries that offer built-in protection against common deserialization vulnerabilities.
  • Schema Validation: Define and enforce schemas for expected data formats to reject malformed or malicious inputs read via Okio.

Attack Surface: Path Traversal via FileSystem Abstraction

• Description: Exploiting Okio's FileSystem abstraction to access files or directories outside the intended scope, potentially leading to unauthorized file access or modification. This occurs when user-controlled input influences file paths used with Okio's FileSystem API.
• Okio Contribution: Okio's FileSystem API, specifically methods like FileSystem.source(Path) and FileSystem.sink(Path), allows applications to interact with file systems. If user input is used to construct Path objects passed to these methods without sanitization, path traversal is possible.
• Example: An application takes a filename from user input and uses it directly in FileSystem.source(Path.get(userInput)) to read a file. An attacker provides input like "../../../../etc/passwd" to bypass intended directory restrictions and access sensitive system files using Okio's file reading capabilities.
• Impact: Information disclosure (reading sensitive files), unauthorized file access, data modification or deletion, potentially leading to system compromise.
• Risk Severity: High
• Mitigation Strategies:
  • Path Sanitization: Sanitize and validate user-provided input used to construct file paths before using them with Okio's FileSystem API.
  • Allow-lists: Use allow-lists to restrict file access to a predefined set of allowed directories or files when using Okio's file operations.
  • Relative Paths: Prefer using relative paths and resolve them against a secure base directory when working with Okio's FileSystem to limit access scope.

Attack Surface: Resource Exhaustion via Large Input Streams

• Description: Causing denial of service by providing extremely large input streams that consume excessive resources (memory, disk space, processing time) when processed by the application using Okio's BufferedSource.
• Okio Contribution: Okio's BufferedSource, while efficient, can still process arbitrarily large streams if the application doesn't impose limits on the data it reads. Uncontrolled reading of large streams via BufferedSource can lead to resource exhaustion.
• Example: An attacker sends an extremely large file to an endpoint that processes it using Okio's BufferedSource. The application attempts to buffer or process this massive stream without limits, leading to memory exhaustion and application crash due to Okio's stream processing.
• Impact: Denial of Service (DoS), application crash, system instability.
• Risk Severity: High
• Mitigation Strategies:
  • Input Size Limits: Implement limits on the maximum size of input streams that the application will process when using Okio's BufferedSource.
  • Streaming Processing: Process data in chunks or streams instead of buffering the entire input in memory when using Okio. Leverage Okio's streaming capabilities effectively.
  • Backpressure: Implement backpressure mechanisms to control the rate at which data is read and processed via Okio, preventing buffer overflows and resource exhaustion.

Attack Surface: Compression and Decompression Vulnerabilities (Zip Bomb/Deflate Bomb)

• Description: Exploiting compression algorithms (like gzip or deflate) to create malicious compressed data (e.g., zip bombs, deflate bombs) that expand to enormous sizes upon decompression, leading to resource exhaustion and denial of service.
• Okio Contribution: Okio provides built-in support for compression and decompression through classes like GzipSource and DeflaterSink. Using these Okio classes to decompress data from untrusted sources makes the application vulnerable to compression bombs.
• Example: An application receives a compressed file from an untrusted source and uses GzipSource to decompress it. The file is a zip bomb, which decompresses to a massive size, consuming all available memory and crashing the application due to uncontrolled decompression via Okio.
• Impact: Denial of Service (DoS), application crash, system instability.
• Risk Severity: High
• Mitigation Strategies:
  • Decompressed Size Limits: Implement strict limits on the maximum decompressed size of data when using Okio's decompression features.
  • Compression Ratio Limits: Monitor the compression ratio during decompression using Okio. Abnormally high ratios can indicate a compression bomb.
  • Streaming Decompression with Resource Monitoring: Use streaming decompression with Okio and continuously monitor resource usage (memory, disk space) during the process. Abort if resource consumption becomes excessive.

Attack Surface: Symlink Exploitation (If FileSystem operations involve symlinks)

• Description: Abuse of symbolic links (symlinks) in file system operations performed using Okio's FileSystem, potentially allowing attackers to bypass access controls or access files outside of intended directories.
• Okio Contribution: Okio's FileSystem abstraction interacts with the underlying file system, including symbolic links. If the application uses Okio's FileSystem to operate on directories containing attacker-controlled symlinks without proper checks, vulnerabilities can arise.
• Example: An application uses Okio's FileSystem to process files within a directory. An attacker creates a symbolic link within that directory pointing to a sensitive file outside of it (e.g., /etc/shadow). When the application traverses the directory using Okio's FileSystem API, it might unintentionally follow the symlink and access the sensitive file.
• Impact: Information disclosure (access to sensitive files), unauthorized file access, potential for privilege escalation or further system compromise.
• Risk Severity: High
• Mitigation Strategies:
  • Avoid Symlink Usage: If possible, design the application to avoid using or processing symbolic links altogether when using Okio's FileSystem.
  • Symlink Resolution Checks: Implement checks to detect and prevent traversal through symbolic links to unintended locations when using Okio's FileSystem. Verify resolved paths are within allowed directories.
  • Canonical Path Resolution: Resolve paths to their canonical form (removing symlinks and relative path components) before using them with Okio's FileSystem to ensure operations are performed on intended files.

Attack Surface: File System Resource Exhaustion (File Descriptor Limits)

• Description: Depletion of file system resources, specifically file descriptors, due to improper management of Source and Sink objects in Okio, especially when dealing with files. Failure to close Okio resources can lead to resource leaks and application failure.
• Okio Contribution: Okio uses Source and Sink interfaces to represent file streams. If these Okio resources are not closed properly after use (e.g., FileSystem.source() or FileSystem.sink() are not closed), file descriptors can be leaked.
• Example: An application opens many files using FileSystem.source() or FileSystem.sink() within a loop but fails to close these Okio Source or Sink objects in error handling paths or due to exceptions. Over time, the application exhausts the available file descriptors, leading to errors, application crashes, or system instability due to improper Okio resource management.
• Impact: Denial of Service (DoS), application crash, system instability, inability to perform file operations.
• Risk Severity: High
• Mitigation Strategies:
  • Proper Resource Management: Ensure that all Okio Source and Sink objects are always properly closed after use, especially in error handling paths and within loops.
  • Try-with-resources (Java/Kotlin): Use try-with-resources blocks (in Java) or Kotlin's use function to automatically close Okio resources when they are no longer needed, even in case of exceptions.
  • Resource Monitoring: Monitor file descriptor usage in production environments to detect potential leaks related to Okio resource management and resource exhaustion issues.