Service Mesh Release Notes

Red Hat OpenShift Service Mesh contains a remotely exploitable vulnerability, CVE-2021-39156, where an HTTP request with a fragment (a section in the end of a URI that begins with a # character) in the URI path could bypass the Istio URI path-based authorization policies. For instance, an Istio authorization policy denies requests sent to the URI path /user/profile. In the vulnerable versions, a request with URI path /user/profile#section1 bypasses the deny policy and routes to the backend (with the normalized URI path /user/profile%23section1), possibly leading to a security incident.

You are impacted by this vulnerability if you use authorization policies with DENY actions and operation.paths, or ALLOW actions and operation.notPaths.

With the mitigation, the fragment part of the request’s URI is removed before the authorization and routing. This prevents a request with a fragment in its URI from bypassing authorization policies which are based on the URI without the fragment part.

Istio generates hostnames for both the hostname itself and all matching ports. For instance, a virtual service or Gateway for a host of "httpbin.foo" generates a config matching "httpbin.foo and httpbin.foo:*". However, exact match authorization policies only match the exact string given for the hosts or notHosts fields.

Your cluster is impacted if you have AuthorizationPolicy resources using exact string comparison for the rule to determine hosts or notHosts.

You must update your authorization policy rules to use prefix match instead of exact match. For example, replacing hosts: ["httpbin.com"] with hosts: ["httpbin.com:*"] in the first AuthorizationPolicy example.

Istio contains a remotely exploitable vulnerability where an HTTP request path with multiple slashes or escaped slash characters (%2F` or %5C`) could potentially bypass an Istio authorization policy when path-based authorization rules are used.

For example, assume an Istio cluster administrator defines an authorization DENY policy to reject the request at path /admin. A request sent to the URL path //admin will NOT be rejected by the authorization policy.

According to RFC 3986, the path //admin with multiple slashes should technically be treated as a different path from the /admin. However, some backend services choose to normalize the URL paths by merging multiple slashes into a single slash. This can result in a bypass of the authorization policy (//admin does not match /admin), and a user can access the resource at path /admin in the backend; this would represent a security incident.

Your cluster is impacted by this vulnerability if you have authorization policies using ALLOW action + notPaths field or DENY action + paths field patterns. These patterns are vulnerable to unexpected policy bypasses.

Your cluster is NOT impacted by this vulnerability if:

Istio authorization policies can be based on the URL paths in the HTTP request. Path normalization, also known as URI normalization, modifies and standardizes the incoming requests' paths so that the normalized paths can be processed in a standard way. Syntactically different paths may be equivalent after path normalization.

Istio supports the following normalization schemes on the request paths before evaluating against the authorization policies and routing the requests:

The normalization algorithms are conducted in the following order:

Ensuring Envoy normalizes request paths to match your backend services' expectations is critical to the security of your system. The following examples can be used as a reference for you to configure your system. The normalized URL paths, or the original URL paths if NONE is selected, will be:

To configure path normalization for Red Hat OpenShift Service Mesh, specify the following in your ServiceMeshControlPlane. Use the configuration examples to help determine the settings for your system.

The fix for CVE-2020-8663: envoy: Resource exhaustion when accepting too many connections added a configurable limit on downstream connections. The configuration option for this limit must be configured to mitigate this vulnerability.

This new configuration option is called overload.global_downstream_max_connections, and it is configurable as a proxy runtime setting. Perform the following steps to configure limits at the Ingress Gateway.