consul/website/content/docs/connect/security.mdx

---
layout: docs
page_title: Service Mesh Security - Best Practices
description: >-
  Consul provides secure service mesh communication by default. Additional configuration can improve network security by preventing unauthorized access and traffic sniffing. Review security considerations, our recommendations, and best practices.
---

# Best Practices for Service Mesh Security

Consul service mesh enables secure service-to-service communication over mutual TLS. This
provides both in-transit data encryption as well as authorization. This page
will document how to secure the service mesh. To try service mesh locally, complete the
[Getting Started guide](/consul/tutorials/kubernetes-deploy/service-mesh?utm_source=docs) or for a full security model reference,
see the dedicated [Consul security model](/consul/docs/security) page. When
setting up service mesh in production, review this [tutorial](/consul/tutorials/developer-mesh/service-mesh-production-checklist?utm_source=consul.io&utm_medium=docs).

Consul service mesh will function in any Consul configuration. However, unless the checklist
below is satisfied, the service mesh is not providing the security guarantees it was
built for. The checklist below can be incrementally adopted towards full
security if you prefer to operate in less secure models initially.

~> **Warning**: The checklist below should not be considered exhaustive. Please
read and understand the [Consul security model](/consul/docs/security)
in depth to assess whether your deployment satisfies the security requirements
of Consul.

## Checklist

### Default Intention Policy Set

Consul should be configured with a default deny intention policy. This forces
all service-to-service communication to be explicitly
allowed via an allow [intention](/consul/docs/connect/intentions).

One advantage of using a default deny policy in combination with specific "allow" rules
is that a failure of intentions due to misconfiguration always results in
_denied_ traffic, rather than unwanted _allowed_ traffic.

In the absence of `default_intention_policy` Consul will fall back to the ACL
default policy when determining whether to allow or deny communications without
an explicit intention.

### Request Normalization Configured for L7 Intentions

~> **Compatibility warning**: This feature is available as of Consul CE 1.20.1 and Consul Enterprise 1.20.1, 1.19.2, 1.18.3, and 1.15.15. We recommend upgrading to the latest version of Consul to take advantage of the latest features and improvements.

Atypical traffic patterns may interfere with the enforcement of L7 intentions. For
example, if a service makes request to a non-normalized URI path and Consul is not
configured to force path normalization, it becomes possible to circumvent path match rules. While a
default deny policy can limit the impact of this issue, we still recommend
that you review your current request normalization configuration. Normalization is critical to avoid unwanted
traffic, especially when using unrecommended security options such as a default allow intentions policy.

Consul adopts a default normalization mode that adheres to [RFC 3986](
https://tools.ietf.org/html/rfc3986#section-6), but additional options to enable stricter
normalization are available in the cluster-wide [Mesh configuration entry](
/consul/docs/connect/config-entries/mesh). We recommend reviewing these options and
enabling the strictest set that does not interfere with application traffic.

We also recommend that you review L7 intention header match rules for potential
issues with multiple header values. Refer to the [service intentions
configuration entry reference](/consul/docs/connect/config-entries/service-intentions#spec-sources-permissions-http-header)
for more information.

You do not need to enable request normalization if you are not using L7 intentions. 
However, normalization may also benefit the use of other service mesh features that 
rely on L7 attribute matching, such as [service routers](/consul/docs/connect/manage-traffic#routing).

### ACLs Enabled with Default Deny

Consul must be configured to use ACLs with a default deny policy. This forces
all requests to have explicit anonymous access or provide an ACL token.

To learn how to enable ACLs, please see the
[tutorial on ACLs](/consul/tutorials/security/access-control-setup-production).

**If ACLs are enabled but are in default allow mode**, then services will be
able to communicate by default. Additionally, if a proper anonymous token
is not configured, this may allow anyone to edit intentions. We do not recommend
this. **If ACLs are not enabled**, deny intentions will still be enforced, but anyone
may edit intentions. This renders the security of the created intentions
effectively useless.

The advantage of a default deny policy in combination with specific "allow" rules
is that at worst, a failure of intentions due to misconfiguration will result in
_denied_ traffic, rather than unwanted _allowed_ traffic.

### TCP and UDP Encryption Enabled

TCP and UDP encryption must be enabled to prevent plaintext communication
between Consul agents. At a minimum, `verify_outgoing` should be enabled
to verify server authenticity with each server having a unique TLS certificate.
`verify_incoming` provides additional agent verification, but doesn't directly
affect service mesh since requests must also always contain a valid ACL token.
Clients calling Consul APIs should be forced over encrypted connections.

See the [Consul agent encryption page](/consul/docs/security/encryption) to
learn more about configuring agent encryption.

**If encryption is not enabled**, a malicious actor can sniff network
traffic or perform a man-in-the-middle attack to steal ACL tokens, always
authorize connections, etc.

### Prevent Unauthorized Access to the Config and Data Directories

The configuration and data directories of the Consul agent on both
clients and servers should be protected from unauthorized access. This
protection must be done outside of Consul via access control systems provided
by your target operating system.

The [full Consul security model](/consul/docs/security) explains the
risk of unauthorized access for both client agents and server agents. In
general, the blast radius of unauthorized access for client agent directories
is much smaller than servers. However, both must be protected against
unauthorized access.

### Prevent Non-Mesh Traffic to Services

For services that are using
[proxies](/consul/docs/connect/proxies)
(are not [natively integrated](/consul/docs/connect/native)),
network access via their unencrypted listeners must be restricted
to only the proxy. This requires at a minimum restricting the listener
to bind to loopback only. More complex solutions may involve using
network namespacing techniques provided by the underlying operating system.

For scenarios where multiple services are running on the same machine
without isolation, these services must all be trusted. We call this the
**trusted multi-tenancy** deployment model. Any service could theoretically
connect to any other service via the loopback listener, bypassing the service mesh
completely. In this scenario, all services must be trusted _or_ isolation
mechanisms must be used.

For developer or operator access to a service, we recommend
using a local service mesh proxy. This is documented in the
[development and debugging guide](/consul/docs/connect/dev).

**If non-proxy traffic can communicate with the service**, this traffic
will not be encrypted or authorized via service mesh.

### Restrict Access to Envoy's Administration Interface

Envoy exposes an **unauthenticated**
[administration interface](https://www.envoyproxy.io/docs/envoy/latest/operations/admin)
that can be used to query and modify the proxy. This interface
allows potentially sensitive information to be retrieved, such as:

* Envoy configuration
* TLS certificates
* List of upstream services and endpoints

We **strongly advise** only exposing the administration interface on a loopback
address (default configuration) and restricting access to a subset of users.

**If the administration interface is exposed externally**, for
example by specifying a routable [`-admin-bind`](/consul/commands/connect/envoy#admin-bind)
address, it may be possible for a malicious actor to gain access to Envoy's
configuration, or impact the service's availability within the cluster.