Announcing Istio 1.1.2 with Important Security Update

Istio 1.1.2 patch release.

Apr 5, 2019

We’re announcing immediate availability of Istio 1.1.2 which contains some important security updates. Please see below for details.

Security update

Two security vulnerabilities have recently been identified in the Envoy proxy (CVE 2019-9900 and CVE 2019-9901). The vulnerabilities have now been patched in Envoy version 1.9.1, and correspondingly in the Envoy builds embedded in Istio 1.1.2 and Istio 1.0.7. Since Envoy is an integral part of Istio, users are advised to update Istio immediately to mitigate security risks arising from these vulnerabilities.

The vulnerabilities are centered on the fact that Envoy did not normalize HTTP URI paths and did not fully validate HTTP/1.1 header values. These vulnerabilities impact Istio features that rely on Envoy to enforce any of authorization, routing, or rate limiting.

Affected Istio releases

The following Istio releases are vulnerable:

Vulnerability impact

CVE 2019-9900 and CVE 2019-9901 allow remote attackers access to unauthorized resources by using specially crafted request URI paths (9901) and NUL bytes in HTTP/1.1 headers (9900), potentially circumventing DoS prevention systems such as rate limiting, or routing to a unexposed upstream system. Refer to issue 6434 and issue 6435 for more information.

As Istio is based on Envoy, Istio customers can be affected by these vulnerabilities based on whether paths and request headers are used within Istio policies or routing rules and how the backend HTTP implementation resolves them. If prefix path matching rules are used by Mixer or by Istio authorization policies or the routing rules, an attacker could exploit these vulnerabilities to gain access to unauthorized paths on certain HTTP backends.


Eliminating the vulnerabilities requires updating to a corrected version of Envoy. We’ve incorporated the necessary updates in the latest Istio patch releases.

For Istio 1.1.x deployments: update to a minimum of Istio 1.1.2

For Istio 1.0.x deployments: update to a minimum of Istio 1.0.7

While Envoy 1.9.1 requires opting in to path normalization to address CVE 2019-9901, the version of Envoy embedded in Istio 1.1.2 and 1.0.7 enables path normalization by default.

Detection of NUL header exploit

Based on current information, this only affects HTTP/1.1 traffic. If this is not structurally possible in your network or configuration, then it is unlikely that this vulnerability applies.

File-based access logging uses the c_str() representation for header values, as does gRPC access logging, so there will be no trivial detection via Envoy’s access logs by scanning for NUL. Instead, operators might look for inconsistencies in logs between the routing that Envoy performs and the logic intended in the RouteConfiguration.

External authorization and rate limit services can check for NULs in headers. Backend servers might have sufficient logging to detect NULs or unintended access; it’s likely that many will simply reject NULs in this scenario via 400 Bad Request, as per RFC 7230.

Detection of path traversal exploit

Envoy’s access logs (whether file-based or gRPC) will contain the unnormalized path, so it is possible to examine these logs to detect suspicious patterns and requests that are incongruous with the intended operator configuration intent. In addition, unnormalized paths are available at ext_authz, rate limiting and backend servers for log inspection.