Defining custom patterns for secret scanning

About custom patterns for secret scanning

You can define custom patterns to identify secrets that are not detected by the default patterns supported by secret scanning. For example, you might have a secret pattern that is internal to your organization. For details of the supported secrets and service providers, see "Secret scanning patterns."

You can define custom patterns for your enterprise, organization, or repository. Secret scanning supports up to 500 custom patterns for each organization or enterprise account, and up to 100 custom patterns per repository.

Regular expression syntax for custom patterns

You can specify custom patterns for secret scanning as one or more regular expressions.

• Secret format: an expression that describes the format of the secret itself.
• Before secret: an expression that describes the characters that come before the secret. By default, this is set to \A|[^0-9A-Za-z] which means that the secret must be at the start of a line or be preceded by a non-alphanumeric character.
• After secret: an expression that describes the characters that come after the secret. By default, this is set to \z|[^0-9A-Za-z] which means that the secret must be followed by a new line or a non-alphanumeric character.
• Additional match requirements: one or more optional expressions that the secret itself must or must not match.

For simple tokens you will usually only need to specify a secret format. The other fields provide flexibility so that you can specify more complex secrets without creating complex regular expressions. For an example of a custom pattern, see "Example of a custom pattern specified using additional requirements" below.

Secret scanning uses the Hyperscan library and only supports Hyperscan regex constructs, which are a subset of PCRE syntax. Hyperscan option modifiers are not supported. For more information on Hyperscan pattern constructs, see "Pattern support" in the Hyperscan documentation.

Defining a custom pattern for a repository

Before defining a custom pattern, you must ensure that secret scanning is enabled on your repository. For more information, see "Configuring secret scanning for your repositories."

1. On your GitHub Enterprise Server instance, navigate to the main page of the repository.

2. Under your repository name, click Settings. If you cannot see the "Settings" tab, select the dropdown menu, then click Settings.

   

3. In the left sidebar, click Security & analysis.

4. Under "Code security and analysis", find "GitHub Advanced Security."

5. Under "Secret scanning", under "Custom patterns", click New pattern.

6. Enter the details for your new custom pattern. You must at least provide the name for your pattern, and a regular expression for the format of your secret pattern.

   1. In the "Pattern name" field, type a name for your pattern.
   2. In the "Secret format" field, type a regular expression for the format of your secret pattern.
   3. You can click More options to provide other surrounding content or additional match requirements for the secret format.
   4. Provide a sample test string to make sure your configuration is matching the patterns you expect.

7. When you're satisfied with your new custom pattern, click Create pattern.

After your pattern is created, secret scanning scans for any secrets in your entire Git history on all branches present in your GitHub repository. For more information on viewing secret scanning alerts, see "Managing alerts from secret scanning."

Example of a custom pattern specified using additional requirements

A company has an internal token with five characteristics. They use the different fields to specify how to identify tokens as follows:

Characteristic	Field and regular expression
Length between 5 and 10 characters	Secret format: [$#%@AA-Za-z0-9]{5,10}
Does not end in a .	After secret: [^\.]
Contains numbers and uppercase letters	Additional requirements: secret must match [A-Z] and [0-9]
Does not include more than one lowercase letter in a row	Additional requirements: secret must not match [a-z]{2,}
Contains one of $%@!	Additional requirements: secret must match [$%@!]

These tokens would match the custom pattern described above:

a9@AAfT!         # Secret string match: a9@AAfT
ee95GG@ZA942@aa  # Secret string match: @ZA942@a
a9@AA!ee9        # Secret string match: a9@AA

These strings would not match the custom pattern described above:

a9@AA.!
a@AAAAA
aa9@AA!ee9
aAAAe9

Defining a custom pattern for an organization

Before defining a custom pattern, you must ensure that you enable secret scanning for the repositories that you want to scan in your organization. To enable secret scanning on all repositories in your organization, see "Managing security and analysis settings for your organization."

1. In the top right corner of GitHub Enterprise Server, click your profile photo, then click Your organizations.

   

2. Next to the organization, click Settings.

3. In the left sidebar, click Security & analysis.

4. Under "Code security and analysis", find "GitHub Advanced Security."

5. Under "Secret scanning", under "Custom patterns", click New pattern.

6. Enter the details for your new custom pattern. You must at least provide the name for your pattern, and a regular expression for the format of your secret pattern.

   1. In the "Pattern name" field, type a name for your pattern.
   2. In the "Secret format" field, type a regular expression for the format of your secret pattern.
   3. You can click More options to provide other surrounding content or additional match requirements for the secret format.
   4. Provide a sample test string to make sure your configuration is matching the patterns you expect.

7. When you're satisfied with your new custom pattern, click Create pattern.

After your pattern is created, secret scanning scans for any secrets in repositories in your organization, including their entire Git history on all branches. Organization owners and repository administrators will be alerted to any secrets found and can review the alert in the repository where the secret is found. For more information on viewing secret scanning alerts, see "Managing alerts from secret scanning."

Defining a custom pattern for an enterprise account

Before defining a custom pattern, you must ensure that you enable secret scanning for your enterprise account. For more information, see "Enabling GitHub Advanced Security for your enterprise."

1. In the top-right corner of GitHub Enterprise Server, click your profile photo, then click Enterprise settings.

   

2. In the enterprise account sidebar, click Policies.

3. Under "Policies", click Advanced Security.

4. Under "GitHub Advanced Security", click the Security features tab.

5. Under "Secret scanning custom patterns", click New pattern.

6. Enter the details for your new custom pattern. You must at least provide the name for your pattern, and a regular expression for the format of your secret pattern.

   1. In the "Pattern name" field, type a name for your pattern.
   2. In the "Secret format" field, type a regular expression for the format of your secret pattern.
   3. You can click More options to provide other surrounding content or additional match requirements for the secret format.
   4. Provide a sample test string to make sure your configuration is matching the patterns you expect.

7. When you're satisfied with your new custom pattern, click Create pattern.

After your pattern is created, secret scanning scans for any secrets in repositories within your enterprise's organizations with GitHub Advanced Security enabled, including their entire Git history on all branches. Organization owners and repository administrators will be alerted to any secrets found, and can review the alert in the repository where the secret is found. For more information on viewing secret scanning alerts, see "Managing alerts from secret scanning."

Editing a custom pattern

When you save a change to a custom pattern, this closes all the secret scanning alerts that were created using the previous version of the pattern.

1. Navigate to where the custom pattern was created. A custom pattern can be created in a repository, organization, or enterprise account.
   • For a repository or organization, display the "Security & analysis" settings for the repository or organization where the custom pattern was created. For more information, see "Defining a custom pattern for a repository" or "Defining a custom pattern for an organization".
   • For an enterprise, under "Policies" display the "Advanced Security" area, and then click Security features. For more information, see "Defining a custom pattern for an enterprise account" above.
2. Under "Secret scanning", to the right of the custom pattern you want to edit, click .
3. When you have reviewed and tested your changes, click Publish changes.

Removing a custom pattern

1. Navigate to where the custom pattern was created. A custom pattern can be created in a repository, organization, or enterprise account.
   • For a repository or organization, display the "Security & analysis" settings for the repository or organization where the custom pattern was created. For more information, see "Defining a custom pattern for a repository" or "Defining a custom pattern for an organization".
   • For an enterprise, under "Policies" display the "Advanced Security" area, and then click Security features. For more information, see "Defining a custom pattern for an enterprise account" above.
2. To the right of the custom pattern you want to remove, click .
3. Review the confirmation, and select a method for dealing with any open alerts relating to the custom pattern.
4. Click Yes, delete this pattern.