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CVE-2021-39155

8.3 · HIGH

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.

Published Aug 24, 2021CWE-178EPSS 1.19%

Overview

CVE-2021-39155 is a high-severity vulnerability. It was published on August 24, 2021 and has a CVSS 3.1 base score of 8.3 (HIGH).

This vulnerability has a CVSS 3.1 base score of 8.3, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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](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](http

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

Refdatatracker.ietf.org/doc/html/rfc4343GitHubgithub.com/istio/istio/security/advisories/GHSA-7774-7vr3-cc8jRefdatatracker.ietf.org/doc/html/rfc4343GitHubgithub.com/istio/istio/security/advisories/GHSA-7774-7vr3-cc8j

How CyberStrike helps

Frequently asked questions

What is CVE-2021-39155?

CVE-2021-39155 is a high-severity vulnerability. It was published on August 24, 2021 and has a CVSS 3.1 base score of 8.3 (HIGH).

How severe is CVE-2021-39155?

This vulnerability has a CVSS 3.1 base score of 8.3, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2021-39155?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2021-39155?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2021-39155 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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