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High severity8.3NVD Advisory· Published Aug 24, 2021· Updated Jun 17, 2026

CVE-2021-39155

CVE-2021-39155

Description

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, 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 guide.

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Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
istio.io/istioGo
< 1.9.81.9.8
istio.io/istioGo
>= 1.10.0, < 1.10.41.10.4
istio.io/istioGo
>= 1.11.0, < 1.11.11.11.1

Affected products

58

Patches

Vulnerability mechanics

References

7

News mentions

0

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