Sensitive Data Detection Basics
Sensitive data such as Social Security numbers, credit card numbers, driver’s license numbers, and so on may be leaked onto the Internet, intentionally or accidentally. The system provides a sensitive data preprocessor that can detect and generate events on sensitive data in ASCII text, which can be particularly useful in detecting accidental data leaks.
Global sensitive data preprocessor options control how the preprocessor functions. You can modify global options that specify the following:
whether the preprocessor replaces all but the last four credit card or Social Security numbers in triggering packets
which destination hosts on your network to monitor for sensitive data
how many total occurrences of all data types in a single session result in an event
Individual data types identify the sensitive data you can detect and generate events on in your specified destination network traffic. You can modify default settings for data type options that specify the following:
a threshold that must be met for a detected data type to generate a single per-session event
the destination ports to monitor for each data type
the application protocols to monitor for each data type
You can create and modify custom data types to detect data patterns that you specify. For example, a hospital might create a data type to protect patient numbers, or a university might create a data type to detect student numbers that have a unique numbering pattern.
The system detects sensitive data per TCP session by matching individual data types against traffic. You can modify the default settings for each data type and for global options that apply to all data types in your intrusion policy. The Firepower System provides predefined, commonly used data types. You can also create custom data types.
A sensitive data preprocessor rule is associated with each data type. You enable sensitive data detection and event generation for each data type by enabling the corresponding preprocessor rule for the data type. A link on the configuration page takes you to a filtered view of sensitive data rules on the Rules page, where you can enable and disable rules and configure other rule attributes.
When you save changes to your intrusion policy, you are given the option to automatically enable the sensitive data preprocessor if the rule associated with a data type is enabled and sensitive data detection is disabled.
The sensitive data preprocessor can detect sensitive data in unencrypted Microsoft Word files that are uploaded and downloaded using FTP or HTTP; this is possible because of the way Word files group ASCII text and formatting commands separately.
The system does not detect encrypted or obfuscated sensitive data, or sensitive data in a compressed or encoded format such as a Base64-encoded email attachment. For example, the system would detect the phone number (555)123-4567, but not an obfuscated version where each number is separated by spaces, as in (5 5 5) 1 2 3 - 4 5 6 7, or by intervening HTML code, such as <b>(555)</b>-<i>123-4567</i>. However, the system would detect, for example, the HTML coded number <b>(555)-123-4567</b> where no intervening codes interrupt the numbering pattern.