CVE-2021-39155: Authorization Policy Bypass Due to Case Insensitive Host Comparison
First published: Tue Aug 24 2021(Updated: )
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.
Credit: security-advisories@github.com security-advisories@github.com
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Istio Istio | <1.9.8 | |
| Istio Istio | >=1.10.0<1.10.4 | |
| Istio Istio | >=1.11.0<1.11.1 |
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Reference Links
Frequently Asked Questions
What is CVE-2021-39155?
CVE-2021-39155 is a vulnerability in Istio, an open source platform for integrating microservices, that allows unauthorized users to bypass authorization policies.
How does CVE-2021-39155 affect Istio?
CVE-2021-39155 affects Istio versions 1.9.8, 1.10.0 to 1.10.4, and 1.11.0 to 1.11.1 on Microsoft Windows Server 2022.
What is the severity of CVE-2021-39155?
CVE-2021-39155 has a severity rating of 7.5 (High).
What is the CWE ID of CVE-2021-39155?
CVE-2021-39155 has a CWE ID of 178.
How can I fix CVE-2021-39155?
To fix CVE-2021-39155, it is recommended to upgrade to a patched version of Istio.
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