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      <title>CVE-2021-39155 — Authorization Policy Bypass Due to Case Insensitive Host Comparison</title>
      <link>https://cve.radiocsirt.org/vuln/cve-2021-39155</link>
      <description>&lt;p&gt;&lt;strong&gt;Affected:&lt;/strong&gt; istio&lt;/p&gt;
&lt;p&gt;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 &amp;#34;httpbin.foo&amp;#34; for some source IPs, but the attacker can bypass this by sending the request with hostname &amp;#34;Httpbin.Foo&amp;#34;. 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.&lt;/p&gt;</description>
      <content:encoded>&lt;p&gt;&lt;strong&gt;Affected:&lt;/strong&gt; istio&lt;/p&gt;
&lt;p&gt;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 &amp;#34;httpbin.foo&amp;#34; for some source IPs, but the attacker can bypass this by sending the request with hostname &amp;#34;Httpbin.Foo&amp;#34;. 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.&lt;/p&gt;</content:encoded>
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