open-vault/website/source/docs/concepts/policies.html.md

layout	page_title	sidebar_current	description
docs	Policies	docs-concepts-policies	Policies are how authorization is done in Vault, allowing you to restrict which parts of Vault a user can access.

Access Control Policies

After authenticating with Vault, the next step is authorization. This is the process of determining what a user is allowed to do. Authorization is unified in Vault in the form of policies.

Policies are HCL or JSON documents that describe what parts of Vault a user is allowed to access. An example of a policy is shown below:

path "sys/*" {
  policy = "deny"
}

path "secret/*" {
  policy = "write"
}

path "secret/foo" {
  policy = "read"
  capabilities = ["create", "sudo"]
}

path "secret/super-secret" {
  capabilities = ["deny"]
}

path "secret/bar" {
  capabilities = ["create"]
  allowed_parameters = {
    "*" = []
  }
  denied_parameters = {
    "foo" = ["bar"]
  }
}

Policies use path based matching to apply rules. A policy may be an exact match, or might be a glob pattern which uses a prefix. Vault operates in a whitelisting mode, so if a path isn't explicitly allowed, Vault will reject access to it. This works well due to Vault's architecture of being like a filesystem: everything has a path associated with it, including the core configuration mechanism under "sys".

~> Policy paths are matched using the most specific defined policy. This may be an exact match or the longest-prefix match of a glob. This means if you define a policy for "secret/foo*", the policy would also match "secret/foobar". The glob character is only supported at the end of the path specification.

Capabilities and Policies

Paths have an associated set of capabilities that provide fine-grained control over operations. The capabilities are:

• create - Create a value at a path. (At present, few parts of Vault distinguish between create and update, so most operations require update. Parts of Vault that provide such a distinction, such as the generic backend, are noted in documentation.)

• read - Read the value at a path.

• update - Change the value at a path. In most parts of Vault, this also includes the ability to create the initial value at the path.

• delete - Delete the value at a path.

• list - List key names at a path. Note that the keys returned by a list operation are not filtered by policies. Do not encode sensitive information in key names.

• sudo - Gain access to paths that are root-protected. This is additive to other capabilities, so a path that requires sudo access will also require read, update, etc. as appropriate.

• deny - No access allowed. This always takes precedence regardless of any other defined capabilities, including sudo.

The only non-obvious capability is sudo. Some routes within Vault and mounted backends are marked as root-protected paths. Clients aren't allowed to access root paths unless they are a root user (have the special policy "root" attached to their token) or have access to that path with 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 is done via root paths. Only root or sudo privilege users are allowed to do this.

Prior to Vault 0.5, the policy keyword was used per path rather than a set of capabilities. In Vault 0.5+ these are still supported as shorthand and to maintain backwards compatibility, but internally they map to a set of capabilities. These mappings are as follows:

• deny - ["deny"]

• sudo - ["create", "read", "update", "delete", "list", "sudo"]

• write - ["create", "read", "update", "delete", "list"]

• read - ["read", "list"]

Fine-Grained Control

There are a few optional fields that allow for fine-grained control over client behavior on a given path. The capabilities associated with this path take precedence over permissions on parameters.

Allowed and Disallowed Parameters

These parameters allow the administrator to restrict the keys (and optionally values) that a user is allowed to specify when calling a path.

• allowed_parameters - A map of keys to an array of values that acts as a whitelist. Setting a key with an [] value will allow changes to parameters with that name. Setting a key with a populated value array (e.g. ["foo", "bar"], [3600, 7200] or [true] will allow that parameter to only be set to one of the values in the array. If any keys exist in the allowed_parameters object all keys not specified will be denied unless there the key "*" is set (mapping to an empty array), which will allow all other parameters to be modified; parameters with specific values will still be restricted to those values.
• denied_parameters - A map of keys to an array of values that acts as a blacklist, and any parameter set here takes precedence over allowed_parameters. Setting to "*" will deny any parameter (so only calls made without specifying any parameters will be allowed). Otherwise setting a key with an [] value will deny any changes to parameters with that name. Setting a key with a populated value array will deny any attempt to set a parameter with that name and value. If keys exist in the denied_parameters object all keys not specified will be allowed (unless allowed_parameters is also set, in which case normal rules will apply).

Required Minimum/Maximum 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 can either be specified as a number of seconds or a string with a s, m, or h suffix indicating seconds, minutes, and hours respectively.

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.

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.

Root Policy

The "root" policy is a special policy that can not be modified or removed. Any user associated with the "root" policy becomes a root user. A root user can do anything within Vault.

There always exists at least one root user (associated with the token when initializing a new server). After this root user, it is recommended to create more strictly controlled users. The original root token should be protected accordingly.

Managing Policies

Policy management can be done via the API or CLI. The CLI commands are vault policies and vault policy-write. Please see the help associated with these commands for more information. They are very easy to use.

Associating Policies

To associate a policy with a user, you must consult the documentation for the authentication backend you're using.

For tokens, they are associated at creation time with vault token-create and the -policy flags. Child tokens can be associated with a subset of a parent's policies. 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 at every token use. 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.