CVE-2021-39156 Explained : Impact and Mitigation

Istio 1.11.0, 1.10.3, and below, as well as 1.9.7 and below, may be susceptible to a vulnerability that allows bypassing Istio's URI path based authorization policies.

Understanding CVE-2021-39156

This CVE highlights a security issue in Istio that could potentially lead to an authorization policy bypass.

What is CVE-2021-39156?

CVE-2021-39156 exposes a security vulnerability in Istio versions that enables an HTTP request with

#fragment

in the path to circumvent authorization policies.

The Impact of CVE-2021-39156

The vulnerability has a CVSS base score of 8.1, indicating a high severity issue. It poses risks of confidentiality, integrity, and requires user interaction for exploitation.

Technical Details of CVE-2021-39156

Istio's flaw is detailed in this section.

Vulnerability Description

The vulnerability allows malicious users to bypass Istio's URI path based authorization policies through specially crafted HTTP requests.

Affected Systems and Versions

Istio versions < 1.9.8
Istio versions >= 1.10.0, < 1.10.4
Istio versions >= 1.11.0, < 1.11.1

Exploitation Mechanism

The vulnerability can be exploited by sending HTTP requests with

#fragment

in the path, tricking the system into unauthorized access.

Mitigation and Prevention

How to address and prevent this security issue.

Immediate Steps to Take

Update Istio to version 1.11.1, 1.10.4, or 1.9.8 that contain patches for this vulnerability.
Consider implementing a Lua filter to normalize the path as a temporary workaround.

Long-Term Security Practices

Regularly check for security updates and apply patches promptly.
Review and adjust authorization policies to enhance security measures.

Patching and Updates

Stay informed about security advisories and release notes for Istio to apply patches and updates promptly.