Advanced Data Scrubbing

In addition to using hooks in your SDK or our server-side data scrubbing features to redact sensitive data, Advanced Data Scrubbing is an alternative way to redact sensitive information just before it is saved in Sentry. It allows you to:

• Define custom regular expressions to match on sensitive data
• Detailed tuning on which parts of an event to scrub
• Partial removal or hashing of sensitive data instead of deletion

A Basic Example

Navigate to your project- or organization-settings, click Security and Privacy, then Advanced Data Scrubbing.

1. Click on Add Rule. You will be presented with a new dialog.
2. Select Mask as Method.
3. Select Credit card numbers as Data Type.
4. Enter $string as Source.

As soon as you press Save, Sentry will attempt to find all credit card numbers in your events going forward, and replace them with a series of ******.

For a more verbose tutorial check out this blogpost.

Rules generally consist of three parts:

• A Method: What to do.
• A Data Type: What to look for.
• A Source: Where to look.

Methods

• Remove: Remove the entire field. We may choose to either set it to null, remove it entirely, or replace it with an empty string depending on technical constraints.
• Mask: Replace all characters with *.
• Hash: Replace the matched substring with a hashed value.
• Replace: Replace the matched substring with a constant placeholder value (defaulting to [Filtered]).

Data Types

• Regex Matches: Custom regular expression. For example: [a-zA-Z0-9]+. Some notes:

  • Do not write /[a-zA-Z0-9]+/g, as that will search for a literal / and /g.
  • For case-insensitivity, prefix your regex with (?i).
  • If you're trying to use one of the popular regex "IDEs" like regex101.com, Golang is usually closest to how Sentry understands your regex.
  • Escape using \, e.g. \* is a literal *. This works for any of the following characters: \.+*?()|[]{}^$.

• Credit Card Numbers: Any substrings that look like credit card numbers.

• Password Fields: Any substrings that look like they may contain passwords. Any string that mentions passwords, auth tokens or credentials, any variable that is called password or auth.

• IP Addresses: Any substrings that look like valid IPv4 or IPv6 addresses.

• IMEI Numbers: Any substrings that look like an IMEI or IMEISV.

• Email Addresses

• UUIDs

• PEM Keys: Any substrings that look like the content of a PEM-keyfile.

• Auth in URLs: Usernames and passwords in URLs like https://user:pass@example.com/foo.

• US social security numbers: 9-digit social security numbers for the USA.

• Usernames in filepaths: For example myuser in /Users/myuser/file.txt, C:\Users\myuser\file.txt, C:\Documents and Settings\myuser\file.txt, /home/myuser/file.txt, ...

• MAC Addresses

• Anything: Matches any value. This is useful if you want to remove a certain JSON key by path using Sources regardless of the value.

Sources

Selectors allow you to restrict rules to certain parts of the event. This is useful to unconditionally remove certain data by event attribute, and can also be used to conservatively test rules on real data. A few examples:

• ** to scrub all default event PII fields (other fields, like the span description, require specific selectors)
• $error.value to scrub in the exception message
• $message to scrub the event-level log message
• extra.'My Value' to scrub the key My Value in "Additional Data"
• extra.** to scrub everything in "Additional Data"
• $http.headers.x-custom-token to scrub the request header X-Custom-Token
• $user.ip_address to scrub the user's IP address
• $frame.vars.foo to scrub a stack trace frame variable called foo
• contexts.device.timezone or contexts.culture.timezone to scrub a key from the Device context
• tags.server_name to scrub the tag server_name

All key names are treated case-insensitively.

Using an event ID to auto-complete sources

Above the Source input field you will find another input field for an event ID. Providing a value there allows for better auto-completion of arbitrary Additional Data fields and variable names.

The event ID is purely optional and the value is not saved as part of your settings. Data scrubbing settings always apply to all new events within a project/organization (going forward).

Advanced source names

Data scrubbing always works on the raw event payload. Keep in mind that some fields in the UI may be called differently in the JSON schema. When looking at an event there should always be a link called "JSON" present that allows you to see what the data scrubber sees.

For example, what is called "Additional Data" in the UI is called extra in the event payload. To remove a specific key called foo, you would write:

[Remove] [Anything] from [extra.foo]

Another example. Sentry knows about two kinds of error messages: the exception message, and the top-level log message. Here is an example of how such an event payload as sent by the SDK (and downloadable from the UI) would look like:

{
  "logentry": {
    "formatted": "Failed to roll out the dinglebop"
  },
  "exception": {
    "values": [
      {
        "type": "ZeroDivisionError",
        "value": "integer division or modulo by zero"
      }
    ]
  }
}

Since the "error message" is taken from the exception's value, and the "message" is taken from logentry, we would have to write the following to remove both from the event:

[Remove] [Anything] from [exception.values.*.value]
[Remove] [Anything] from [logentry.formatted]

Boolean Logic

You can combine sources using boolean logic.

• Prefix with ! to invert the source. foo matches the JSON key foo, while !foo matches everything but foo.
• Build the conjunction (AND) using &&, such as: foo && !extra.foo to match the key foo except when inside of extra.
• Build the disjunction (OR) using ||, such as: foo || bar to match foo or bar.

Wildcards

• ** matches all subpaths, so that foo.** matches all JSON keys within foo.
• * matches a single path item, so that foo.* matches all JSON keys one level below foo.

Value Types

Select subsections by JSON-type using the following:

• $string: Matches any string value
• $number: Matches any integer or float value
• $datetime: Matches any field in the event that represents a timestamp
• $array: Matches any JSON array value
• $object: Matches any JSON object

Select known parts of the schema using the following:

• $error: Matches a single exception instance. Alias for exception.values.*
• $stack: Matches a stack trace instance. Alias for stacktrace || $error.stacktrace || $thread.stacktrace
• $frame: Matches a frame in a stack trace. Alias for $stacktrace.frames.*
• $http: Matches the HTTP request context of an event. Alias for request
• $user: Matches the user context of an event. Alias for user
• $message: Matches the top-level log message. Alias for $logentry.formatted
• $logentry: Matches the logentry attribute of an event. Alias for logentry
• $thread: Matches a single thread instance. Alias for threads.values.*
• $breadcrumb: Matches a single breadcrumb. Alias for breadcrumbs.values.*
• $span: Matches a trace span. Alias for spans.*
• $sdk: Matches the SDK context. Alias for sdk

Select attachment and parts of attachments, see Attachment Scrubbing for details.

• $attachments: Root selector for attachments.
• $minidump: Selector for minidump attachments.
• $binary: Matches all binary data fields in attachments.

Escaping Special Characters

If the object key you want to match contains whitespace or special characters, you can use quotes to escape it:

[Remove] [Anything] from [extra.'my special value']

This matches the key my special value in Additional Data.

To escape ' (single quote) within the quotes, replace it with '' (two quotes):

[Remove] [Anything] from [extra.'my special '' value']

This matches the key my special ' value in Additional Data.

Known Limitations of server-side data scrubbing

The following limitations generally apply to all server-side data scrubbing, be it basic Safe Fields usage or Advanced Data Scrubbing.

• Hashing, masking or replacing a JSON object, array or number (anything that is not a string) cannot be done in all circumstances as it would change the JSON type of the value and violate assumptions Sentry's internals make about the data schema. Data scrubbing will ignore the Method in those cases and always remove/replace with null as that is always safe.

• Sentry's internals require that the event user's IP address must either be null or a valid IPv4/IPv6 address. If you're trying to hash, mask or replace IP addresses, data scrubbing will move the replacement value into the user ID (if one is not already set) in order to avoid breaking this requirement while still providing useful data for the Users count on an issue.

• In stack traces, scrubbing works on file paths but not on a file's base name. This would violate assumptions in the processing pipeline resulting in a poor user experience. Instead, you can scrub a file's base name in the SDK itself, using the RewriteFrames integration or beforeSend.