attack-surface.md

Attack Surface Analysis for kotlin/kotlinx-datetime

Attack Surface: 1. Untrusted Input to Parsing Functions

• Description: Maliciously crafted date/time strings provided as input to parsing functions can lead to unexpected behavior, exceptions, or potentially resource exhaustion. This is the most significant attack vector directly related to the library.
  • How kotlinx-datetime Contributes: The library's parsing functions (Instant.parse(), LocalDate.parse(), LocalDateTime.parse(), TimeZone.of(), etc.) are the direct targets of this attack. The library's internal parsing logic is where a vulnerability would reside.
  • Example:
    • An attacker provides an extremely long and complex string designed to consume excessive CPU resources during parsing (DoS): "2023-10-27T..................................................................[thousands of dots]................................................Z"
    • An attacker provides a string that exploits a hypothetical (but possible) bug in the parsing logic to cause an unexpected internal state or crash. This is highly dependent on the specific implementation and any undiscovered vulnerabilities. Example (hypothetical, not a known vulnerability): "99999999999999999999-12-31T23:59:59.999999999Z" (exploiting a potential integer overflow in year handling).
    • An attacker provides a malformed timezone string to TimeZone.of(): !!INVALID!!TIME!!ZONE!!
  • Impact:
    • Denial of Service (DoS): The application becomes unresponsive or crashes due to excessive resource consumption.
    • Unexpected Application Behavior: Incorrect date/time values are processed, leading to logic errors in the application.
    • Potentially (though less likely) Information Disclosure: In a very specific, undiscovered vulnerability scenario, carefully crafted input might expose internal memory or state information. This is a much lower probability than DoS.
  • Risk Severity: High (DoS is a realistic concern; other impacts are less likely but still possible). Could be Critical depending on the application's reliance on date/time data and the specific vulnerability exploited. If date/time parsing is used in a security-critical context (e.g., authentication, authorization, expiry checks), a vulnerability could have critical consequences.
  • Mitigation Strategies:
    • Strict Input Validation: Crucially, before calling any kotlinx-datetime parsing function, validate the input string against a strict and predefined format using regular expressions or a dedicated validation library. This is the primary defense. Do not rely on the library's exceptions alone. For example:

      val iso8601Regex = Regex("""^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(\.\d+)?Z$""")
      val userInput = getUserInput() // Get input from an untrusted source
      
      if (iso8601Regex.matches(userInput)) {
          try {
              val instant = Instant.parse(userInput)
              // ... process the instant ...
          } catch (e: DateTimeParseException) {
              // Handle parsing errors (log, report, etc.) - input was valid format, but still unparseable
              logError("DateTimeParseException: ${e.message}, Input: $userInput")
              showUserFriendlyErrorMessage()
          }
      } else {
          // Handle invalid format (log, report, etc.)
          logError("Invalid date/time format: $userInput")
          showUserFriendlyErrorMessage()
      }
      
      val timeZoneRegex = Regex("^[A-Za-z/\\+\\-0-9_]+$") // Basic validation, refine as needed
      val userTimeZone = getUserTimeZoneInput()
       if (timeZoneRegex.matches(userTimeZone)) {
          try{
              val timeZone = TimeZone.of(userTimeZone)
          }
          catch (e: IllegalTimeZoneException){
              //Handle exception
          }
       }
       else{
          //Handle invalid format
       }

    • Format Specificity: Use the most specific parsing format possible. If you know the input should always be in a particular ISO 8601 variant, use a DateTimeFormatter configured for that specific variant.
    • Resource Limits: Implement timeouts and maximum input length restrictions when parsing untrusted data. This prevents an attacker from providing excessively long strings designed to cause resource exhaustion. Use Kotlin coroutines with timeouts:

      import kotlinx.coroutines.*
      
      runBlocking {
          try {
              withTimeout(1000) { // 1-second timeout
                  val instant = Instant.parse(veryLongInputString)
                  // ...
              }
          } catch (e: TimeoutCancellationException) {
              // Handle timeout
              logError("Parsing timed out!")
          }
      }

    • Exception Handling: Always wrap parsing calls in try-catch blocks. Log the original input and the exception details for debugging and auditing. Never expose raw exception messages to the user.
    • Fuzz Testing: Use fuzz testing tools to automatically generate a large number of invalid and edge-case inputs to test the robustness of your parsing logic and your input validation.
    • Whitelist Timezones: If accepting timezone input, validate against a whitelist.

      val allowedTimeZones = setOf("UTC", "America/Los_Angeles", "Europe/London") // Example whitelist
      val userTimeZone = getUserTimeZoneInput()
      
      if (userTimeZone in allowedTimeZones) {
          val timeZone = TimeZone.of(userTimeZone)
          // ...
      } else {
          // Handle invalid time zone
      }

Attack Surface: 2. Denial of Service via Resource Exhaustion (Parsing)

• Description: Specifically targeting resource exhaustion by providing extremely complex or long input strings to parsing functions.
  • How kotlinx-datetime Contributes: The parsing functions are the direct target. The complexity of the parsing algorithm and its handling of large inputs determine the vulnerability.
  • Example: As above, an extremely long string filled with many delimiters or special characters.
  • Impact: Denial of Service (DoS) – the application becomes unresponsive.
  • Risk Severity: High. DoS is a readily achievable attack if input validation and resource limits are not in place.
  • Mitigation Strategies: Identical to those listed for #1, with particular emphasis on input length limits and timeouts.