Policies

Everything in Vault is path-based, and policies are no exception. Policies provide a declarative way to grant or forbid access to certain paths and operations in Vault. This section discusses policy workflows and syntaxes.

Policies are deny by default, so an empty policy grants no permission in the system.

Policy-authorization workflow

Before a human or machine can gain access, an administrator must configure Vault with an auth method. Authentication is the process by which human or machine-supplied information is verified against an internal or external system.

Consider the following diagram, which illustrates the steps a security team would take to configure Vault to authenticate using a corporate LDAP or ActiveDirectory installation. Even though this example uses LDAP, the concept applies to all auth methods.

1. The security team configures Vault to connect to an auth method. This configuration varies by auth method. In the case of LDAP, Vault needs to know the address of the LDAP server and whether to connect using TLS. It is important to note that Vault does not store a copy of the LDAP database - Vault will delegate the authentication to the auth method.

2. The security team authors a policy (or uses an existing policy) which grants access to paths in Vault. Policies are written in HCL in your editor of preference and saved to disk.

3. The policy's contents are uploaded and stored in Vault and referenced by name. You can think of the policy's name as a pointer or symlink to its set of rules.

4. Most importantly, the security team maps data in the auth method to a policy. For example, the security team might create mappings like:

   Members of the OU group "dev" map to the Vault policy named "readonly-dev".

   or

   Members of the OU group "ops" map to the Vault policies "admin" and "auditor".

Now Vault has an internal mapping between a backend authentication system and internal policy. When a user authenticates to Vault, the actual authentication is delegated to the auth method. As a user, the flow looks like:

1. A user attempts to authenticate to Vault using their LDAP credentials, providing Vault with their LDAP username and password.

2. Vault establishes a connection to LDAP and asks the LDAP server to verify the given credentials. Assuming this is successful, the LDAP server returns the information about the user, including the OU groups.

3. Vault maps the result from the LDAP server to policies inside Vault using the mapping configured by the security team in the previous section. Vault then generates a token and attaches the matching policies.

4. Vault returns the token to the user. This token has the correct policies assigned, as dictated by the mapping configuration that was setup by the security team in advance.

The user then uses this Vault token for future operations. If the user performs the authentication steps again, they will get a new token. The token will have the same permissions, but the actual token will be different. Authenticating a second time does not invalidate the original token.

Policy syntax

Policies are written in HCL or JSON and describe which paths in Vault a user or machine is allowed to access.

Here is a very simple policy which grants read capabilities to the KVv1 path "secret/foo":

path "secret/foo" {
  capabilities = ["read"]
}

When this policy is assigned to a token, the token can read from "secret/foo". However, the token cannot update or delete "secret/foo", since the capabilities do not allow it. Because policies are deny by default, the token would have no other access in Vault.

Here is a more detailed policy, and it is documented inline:

# This section grants all access on "secret/*". further restrictions can be
# applied to this broad policy, as shown below.
path "secret/*" {
  capabilities = ["create", "read", "update", "patch", "delete", "list"]
}

# Even though we allowed secret/*, this line explicitly denies
# secret/super-secret. this takes precedence.
path "secret/super-secret" {
  capabilities = ["deny"]
}

# Policies can also specify allowed, disallowed, and required parameters. here
# the key "secret/restricted" can only contain "foo" (any value) and "bar" (one
# of "zip" or "zap").
path "secret/restricted" {
  capabilities = ["create"]
  allowed_parameters = {
    "foo" = []
    "bar" = ["zip", "zap"]
  }
}

Policies use path-based matching to test the set of capabilities against a request. A policy path may specify an exact path to match, or it could specify a glob pattern which instructs Vault to use a prefix match:

# Permit reading only "secret/foo". an attached token cannot read "secret/food"
# or "secret/foo/bar".
path "secret/foo" {
  capabilities = ["read"]
}

# Permit reading everything under "secret/bar". an attached token could read
# "secret/bar/zip", "secret/bar/zip/zap", but not "secret/bars/zip".
path "secret/bar/*" {
  capabilities = ["read"]
}

# Permit reading everything prefixed with "zip-". an attached token could read
# "secret/zip-zap" or "secret/zip-zap/zong", but not "secret/zip/zap
path "secret/zip-*" {
  capabilities = ["read"]
}

In addition, a + can be used to denote any number of characters bounded within a single path segment (this appeared in Vault 1.1):

# Permit reading the "teamb" path under any top-level path under secret/
path "secret/+/teamb" {
  capabilities = ["read"]
}

# Permit reading secret/foo/bar/teamb, secret/bar/foo/teamb, etc.
path "secret/+/+/teamb" {
  capabilities = ["read"]
}

Vault's architecture is similar to a filesystem. Every action in Vault has a corresponding path and capability - even Vault's internal core configuration endpoints live under the "sys/" path. Policies define access to these paths and capabilities, which controls a token's access to credentials in Vault.

Priority matching

This means if you define a policy for "secret/foo*", the policy would also match "secret/foobar". Specifically, when there are potentially multiple matching policy paths, P1 and P2, the following matching criteria is applied:

1. If the first wildcard (+) or glob (*) occurs earlier in P1, P1 is lower priority
2. If P1 ends in * and P2 doesn't, P1 is lower priority
3. If P1 has more + (wildcard) segments, P1 is lower priority
4. If P1 is shorter, it is lower priority
5. If P1 is smaller lexicographically, it is lower priority

For example, given the two paths, "secret/*" and "secret/+/+/foo/*", the first wildcard appears in the same place, both end in * and the latter has two wildcard segments while the former has zero. So we end at rule (3), and give "secret/+/+/foo/*" lower priority.

When providing list capability, it is important to note that since listing always operates on a prefix, policies must operate on a prefix because Vault will sanitize request paths to be prefixes.

Capabilities

Each path must define one or more capabilities which provide fine-grained control over permitted (or denied) operations. As shown in the examples above, capabilities are always specified as a list of strings, even if there is only one capability.

To determine the capabilities needed to perform a specific operation, the -output-policy flag can be added to the CLI subcommand. For an example, refer to the Print Policy Requirements document section.

The list of capabilities include the following:

• create (POST/PUT) - Allows creating data at the given path. Very few parts of Vault distinguish between create and update, so most operations require both create and update capabilities. Parts of Vault that provide such a distinction are noted in documentation.

• read (GET) - Allows reading the data at the given path.

• update (POST/PUT) - Allows changing the data at the given path. In most parts of Vault, this implicitly includes the ability to create the initial value at the path.

• patch (PATCH) - Allows partial updates to the data at a given path.

• delete (DELETE) - Allows deleting the data at the given path.

• list (LIST) - Allows listing values at the given path. Note that the keys returned by a list operation are not filtered by policies. Do not encode sensitive information in key names. Not all backends support listing.

In the list above, the associated HTTP verbs are shown in parenthesis next to the capability. When authoring policy, it is usually helpful to look at the HTTP API documentation for the paths and HTTP verbs and map them back onto capabilities. While the mapping is not strictly 1:1, they are often very similarly matched.

In addition to the standard set, there are some capabilities that do not map to HTTP verbs.

• sudo - Allows access to paths that are root-protected. Tokens are not permitted to interact with these paths unless they have the sudo capability (in addition to the other necessary capabilities for performing an operation against that path, such as read or delete).

  For example, modifying the audit log backends requires a token with sudo privileges.

• deny - Disallows access. This always takes precedence regardless of any other defined capabilities, including sudo.

• subscribe - Allows subscribing to events for the given path.

Templated policies

The policy syntax allows for doing variable replacement in some policy strings with values available to the token. Currently identity information can be injected, and currently the path keys in policies allow injection.

Parameters

Examples

The following policy creates a section of the KVv2 Secret Engine to a specific user

path "secret/data/{{identity.entity.id}}/*" {
  capabilities = ["create", "update", "patch", "read", "delete"]
}

path "secret/metadata/{{identity.entity.id}}/*" {
  capabilities = ["list"]
}

If you wanted to create a shared section of KV that is associated with entities that are in a group.

# In the example below, the group ID maps a group and the path
path "secret/data/groups/{{identity.groups.ids.fb036ebc-2f62-4124-9503-42aa7A869741.name}}/*" {
  capabilities = ["create", "update", "patch", "read", "delete"]
}

path "secret/metadata/groups/{{identity.groups.ids.fb036ebc-2f62-4124-9503-42aa7A869741.name}}/*" {
  capabilities = ["list"]
}

If you want to use the metadata associated with an authentication plugin in your templates, you will need to get its mount accessor and access it via the aliases key.

You can get the mount accessor value using the following command:

$> vault auth list
Path           Type          Accessor                    Description
----           ----          --------                    -----------
kubernetes/    kubernetes    auth_kubernetes_xxxx        n/a
token/         token         auth_token_yyyy             token based credentials

The following templated policy allow to read the path associated with the Kubernetes service account namespace of the identity:

path "secret/data/{{identity.entity.aliases.auth_kubernetes_xxxx.metadata.service_account_namespace}}/*" {
  capabilities = ["read"]
}

Fine-grained control

In addition to the standard set of capabilities, Vault offers finer-grained control over permissions at a given path. The capabilities associated with a path take precedence over permissions on parameters.

Parameter constraints

See the API Specification for more information.

Policies can take into account HTTP request parameters to further constrain requests, using the following options:

• required_parameters - A list of parameters that must be specified.

  # This requires the user to create "secret/profile" with a parameter/key named
  # "name" and "id" where kv v1 is enabled at "secret/".
  path "secret/profile" {
    capabilities = ["create"]
    required_parameters = ["name", "id"]
  }
  

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• allowed_parameters - A list of keys and values that are permitted on the given path.

  • Setting a parameter with a value of the empty list allows the parameter to contain any value.

    # This allows the user to update the password parameter value set on any
    # users configured for userpass auth method. The password value can be
    # anything. However, the user cannot update other parameter values such as
    # token_ttl.
    path "auth/userpass/users/*" {
      capabilities = ["update"]
      allowed_parameters = {
        "password" = []
      }
    }
    

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    Usage example: The ACL Policy Path Templating tutorial demonstrates the use of allowed_parameters to permit a user to update the user's password when using the userpass auth method to log in with Vault.

  • Setting a parameter with a value of a populated list allows the parameter to contain only those values.

    # This allows the user to create or update an encryption key for transit
    # secrets engine enabled at "transit/". When you do, you can set the
    # "auto_rotate_period" parameter value so that the key gets rotated.
    # However, the rotation period must be "8h", "24h", or "5d". Any other value
    # will result in an error.
    path "transit/keys/*" {
      capabilities = ["create", "update"]
      allowed_parameters = {
        "auto_rotate_period" = ["8h", "24h", "5d"]
      }
    }
    

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  • If any keys are specified, all non-specified parameters will be denied unless the parameter "*" is set to an empty array, which will allow all other parameters to be modified. Parameters with specific values will still be restricted to those values.

    # When kv v1 secrets engine is enabled at "secret/", this allows the user to
    # create "secret/foo" with a parameter named "bar". The parameter "bar" can
    # only contain the values "zip" or "zap", but any other parameters may be
    # created with any value.
    path "secret/foo" {
      capabilities = ["create"]
      allowed_parameters = {
        "bar" = ["zip", "zap"]
        "*"   = []
      }
    }
    

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• denied_parameters - A list of keys and values that are not permitted on the given path. Any values specified here take precedence over allowed_parameters.

  • Setting a parameter with a value of the empty list denies any changes to that parameter.

    # This allows the user to update the userpass auth method's user
    # configurations (e.g., "password") but cannot update the "token_policies"
    # and "policies" parameter values.
    path "auth/userpass/users/*" {
      capabilities = ["update"]
      denied_parameters = {
        "token_policies" = []
        "policies" = []
      }
    }
    

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  • Setting a parameter with a value of a populated list denies any parameter containing those values.

    # This allows the user to create or update token roles. However, the
    # "allowed_policies" parameter value cannot be "admin", but the user can
    # assign any other policies to the parameter.
    path "auth/token/roles/*" {
      capabilities = ["create", "update"]
      denied_parameters = {
        "allowed_policies" = ["admin"]
      }
    }
    

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  • Setting to "*" will deny any parameter.

    # This allows the user to create or update an encryption key for transit
    # secrets engine enabled at "transit/". However, the user cannot set any of
    # the configuration parameters. As a result, the created key will have all
    # parameters set to default values.
    path "transit/keys/*" {
      capabilities = ["create", "update"]
      denied_parameters = {
        "*" = []
      }
    }
    

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  • If any parameters are specified, all non-specified parameters are allowed, unless allowed_parameters is also set, in which case normal rules apply.

Parameter values also support prefix/suffix globbing. Globbing is enabled by prepending or appending or prepending a splat (*) to the value:

# Only allow a parameter named "bar" with a value starting with "foo-*".
path "secret/foo" {
  capabilities = ["create"]
  allowed_parameters = {
    "bar" = ["foo-*"]
  }
}

Parameter constraints limitations

Default values

Evaluation of policies with allowed_parameters, denied_parameters, and required_parameters happens without consideration of parameters' default values.

Given the following policy:

# The "no_store" parameter cannot be false
path "secret/foo" {
  capabilities = ["create"]
  denied_parameters = {
    "no_store" = [false, "false"]
  }
}

The following operation will error, because "no_store" is set to false:

$ vault write secret/foo no_store=false value=bar

Whereas the following operation will succeed, even if the "no_store" parameter must be a boolean, and it defaults to false:

# Succeeds because "no_store=false" isn't present in the parameters
$ vault write secret/foo value=bar

This is because the policy evaluator does not know what the default value is for the "no_store" parameter. All it sees is that the denied parameter isn't present in the command.

This can be resolved by requiring the "no_store" parameter in your policy:

path "secret/foo" {
  capabilities = ["create"]
  required_parameters = ["no_store"]
  denied_parameters = {
    "no_store" = [false, "false"]
  }
}

The following command, which previously succeeded, will now fail under the new policy because there is no "no_store" parameter:

$ vault write secret/foo value=bar

Globbing

It's also important to note that the use of globbing may result in surprising or unexpected behavior:

# This allows the user to create, update, or patch "secret/foo" with a parameter
# named "bar". the values passed to parameter "bar" must start with "baz/"
# so values like "baz/quux" are fine. however, values like
# "baz/quux,wibble,wobble,wubble" would also be accepted. the API that
# underlies "secret/foo" might allow comma delimited values for the "bar"
# parameter, and if it did, specifying a value like
# "baz/quux,wibble,wobble,wubble" would result in 4 different values getting
# passed along. seeing values like "wibble" or "wobble" getting passed to
# "secret/foo" might surprise someone that expected the allowed_parameters
# constraint to only allow values starting with "baz/".
path "secret/foo" {
  capabilities = ["create", "update", "patch"]
  allowed_parameters = {
    "bar" = ["baz/*"]
  }
}

Required response wrapping TTLs

These parameters can be used to set minimums/maximums on TTLs set by clients when requesting that a response be wrapped, with a granularity of a second. These use duration format strings.

In practice, setting a minimum TTL of one second effectively makes response wrapping mandatory for a particular path.

• min_wrapping_ttl - The minimum allowed TTL that clients can specify for a wrapped response. In practice, setting a minimum TTL of one second effectively makes response wrapping mandatory for a particular path. It can also be used to ensure that the TTL is not too low, leading to end targets being unable to unwrap before the token expires.

• max_wrapping_ttl - The maximum allowed TTL that clients can specify for a wrapped response.

# This effectively makes response wrapping mandatory for this path by setting min_wrapping_ttl to 1 second.
# This also sets this path's wrapped response maximum allowed TTL to 90 seconds.
path "auth/approle/role/my-role/secret-id" {
    capabilities = ["create", "update"]
    min_wrapping_ttl = "1s"
    max_wrapping_ttl = "90s"
}

If both are specified, the minimum value must be less than the maximum. In addition, if paths are merged from different stanzas, the lowest value specified for each is the value that will result, in line with the idea of keeping token lifetimes as short as possible.

Built-in policies

Vault has two built-in policies: default and root. This section describes the two built-in policies.

Default policy

The default policy is a built-in Vault policy that cannot be removed. By default, it is attached to all tokens, but may be explicitly excluded at token creation time by supporting authentication methods.

The policy contains basic functionality such as the ability for the token to look up data about itself and to use its cubbyhole data. However, Vault is not prescriptive about its contents. It can be modified to suit your needs; Vault will never overwrite your modifications. If you want to stay up-to-date with the latest upstream version of the default policy, simply read the contents of the policy from an up-to-date dev server, and write those contents into your Vault's default policy.

To view all permissions granted by the default policy on your Vault installation, run:

$ vault read sys/policy/default

To disable attachment of the default policy:

$ vault token create -no-default-policy

or via the API:

$ curl \
  --request POST \
  --header "X-Vault-Token: ..." \
  --data '{"no_default_policy": "true"}' \
  https://vault.hashicorp.rocks/v1/auth/token/create

Root policy

The root policy is a built-in Vault policy that cannot be modified or removed. Any user associated with this policy becomes a root user. A root user can do anything within Vault. As such, it is highly recommended that you revoke any root tokens before running Vault in production.

When a Vault server is first initialized, there always exists one root user. This user is used to do the initial configuration and setup of Vault. After configured, the initial root token should be revoked and more strictly controlled users and authentication should be used.

To revoke a root token, run:

$ vault token revoke "<token>"

or via the API:

$ curl \
  --request POST \
  --header "X-Vault-Token: ..." \
  --data '{"token": "<token>"}' \
  https://vault.hashicorp.rocks/v1/auth/token/revoke

For more information, please read:

• Production Hardening
• Generating a Root Token

Managing policies

Policies are authored (written) in your editor of choice. They can be authored in HCL or JSON, and the syntax is described in detail above. Once saved, policies must be uploaded to Vault before they can be used.

Listing policies

To list all registered policies in Vault:

$ vault read sys/policy

or via the API:

$ curl \
  --header "X-Vault-Token: ..." \
  https://vault.hashicorp.rocks/v1/sys/policy

Creating policies

Policies may be created (uploaded) via the CLI or via the API. To create a new policy in Vault:

$ vault policy write policy-name policy-file.hcl

or via the API:

$ curl \
  --request POST \
  --header "X-Vault-Token: ..." \
  --data '{"policy":"path \"...\" {...} "}' \
  https://vault.hashicorp.rocks/v1/sys/policy/policy-name

In both examples, the name of the policy is "policy-name". You can think of this name as a pointer or symlink to the policy ACLs. Tokens are attached policies by name, which are then mapped to the set of rules corresponding to that name.

Updating policies

Existing policies may be updated to change permissions via the CLI or via the API. To update an existing policy in Vault, follow the same steps as creating a policy, but use an existing policy name:

$ vault write sys/policy/my-existing-policy policy=@updated-policy.json

or via the API:

$ curl \
  --request POST \
  --header "X-Vault-Token: ..." \
  --data '{"policy":"path \"...\" {...} "}' \
  https://vault.hashicorp.rocks/v1/sys/policy/my-existing-policy

Deleting policies

Existing policies may be deleted via the CLI or API. To delete a policy:

$ vault delete sys/policy/policy-name

or via the API:

$ curl \
  --request DELETE \
  --header "X-Vault-Token: ..." \
  https://vault.hashicorp.rocks/v1/sys/policy/policy-name

This is an idempotent operation. Vault will not return an error when deleting a policy that does not exist.

Associating policies

Vault can automatically associate a set of policies to a token based on an authorization. This configuration varies significantly between authentication backends. For simplicity, this example will use Vault's built-in userpass auth method.

A Vault administrator or someone from the security team would create the user in Vault with a list of associated policies:

$ vault write auth/userpass/users/sethvargo \
    password="s3cr3t!" \
    policies="dev-readonly,logs"

This creates an authentication mapping to the policy such that, when the user authenticates successfully to Vault, they will be given a token which has the list of policies attached.

The user wishing to authenticate would run

$ vault login -method="userpass" username="sethvargo"
Password (will be hidden): ...

If the provided information is correct, Vault will generate a token, assign the list of configured policies to the token, and return that token to the authenticated user.

Root protected API endpoints

The following paths requires a root token or sudo capability in the policy:

Tokens

Tokens have two sets of policies: identity policies, which are computed based on the entity and its groups, and token policies, which are either defined based on the login method or, in the case of explicit token creates via the API, are an input to the token creation. What follows concerns token policies exclusively: a token's identity policies cannot be controlled except by modifying the underlying entities, groups, and group memberships.

Tokens are associated with their policies at creation time. For example:

$ vault token create -policy=dev-readonly -policy=logs

Normally the only policies that may be specified are those which are present in the current token's (i.e. the new token's parent's) token policies. However, root users can assign any policies.

There is no way to modify the policies associated with a token once the token has been issued. The token must be revoked and a new one acquired to receive a new set of policies.

However, the contents of policies are parsed in real-time whenever the token is used. As a result, if a policy is modified, the modified rules will be in force the next time a token, with that policy attached, is used to make a call to Vault.

Tutorial

Refer to the following tutorials for further learning:

• Vault Policies
• ACL Policy Path Templating