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EUVD-2026-30448

fkie_cve-2021-39155

Istio is an open source platform for providing a uniform way to integrate microservices, manage traffic flow across microservices, enforce policies and aggregate telemetry data. According to [RFC 4343](https://datatracker.ietf.org/doc/html/rfc4343), Istio authorization policy should compare the hostname in the HTTP Host header in a case insensitive way, but currently the comparison is case sensitive. The proxy will route the request hostname in a case-insensitive way which means the authorization policy could be bypassed. As an example, the user may have an authorization policy that rejects request with hostname "httpbin.foo" for some source IPs, but the attacker can bypass this by sending the request with hostname "Httpbin.Foo". Patches are available in Istio 1.11.1, Istio 1.10.4 and Istio 1.9.8. As a work around a Lua filter may be written to normalize Host header before the authorization check. This is similar to the Path normalization presented in the [Security Best Practices](https://istio.io/latest/docs/ops/best-practices/security/#case-normalization) guide.

GHSA-7774-7vr3-cc8j — Authorization Policy Bypass Due to Case Insensitive Host Comparison

Affected: Go: istio.io/istio

### Impact According to [RFC 4343](https://datatracker.ietf.org/doc/html/rfc4343), Istio authorization policy should compare the hostname in the HTTP Host header in a case insensitive way, but currently the comparison is case sensitive. The Envoy proxy will route the request hostname in a case-insensitive way which means the authorization policy could be bypassed. As an example, the user may have an authorization policy that rejects request with hostname "httpbin.foo" for some source IPs, but the attacker can bypass this by sending the request with hostname "Httpbin.Foo".

### Patches * Istio 1.11.1 and above * Istio 1.10.4 and above * Istio 1.9.8 and above

### Workarounds A Lua filter may be written to normalize Host header before the authorization check. This is similar to the Path normalization presented in the [Security Best Practices](https://istio.io/latest/docs/ops/best-practices/security/#case-normalization) guide.

### References More details can be found in the [Istio Security Bulletin](https://istio.io/latest/news/security/istio-security-2021-008).

### For more information If you have any questions or comments about this advisory, please email us at istio-security-vulnerability-reports@googlegroups.com

gsd-2021-39155

RHSA-2021:3272 — Red Hat Security Advisory: Red Hat OpenShift Service Mesh 2.0.7.1 security update

envoyproxy/envoy: HTTP request with multiple value headers can bypass authorization policies envoyproxy/envoy: HTTP request with a URL fragment in the URI can bypass authorization policies envoyproxy/envoy: denial of service when using extensions that modify request or response sizes istio/istio: HTTP request can bypass authorization mechanisms due to case insensitive host comparison istio/istio: HTTP request with fragment in URI can bypass authorization mechanisms