Authorization Policy Bypass in Istio by Envoy RBAC Header Matching
CVE-2026-31838

6.9MEDIUM

Key Information:

Vendor

Istio

Status
Istio
Vendor
CVE Published:
10 March 2026

What is CVE-2026-31838?

A flaw in Envoy's Role-Based Access Control (RBAC) header matching in Istio allows for an authorization policy bypass, particularly when HTTP headers can have multiple values. Attackers can exploit this vulnerability by crafting specific requests that lead Envoy to misinterpret the intended header values, thereby circumventing established authorization checks. As a result, unauthorized requests may gain access to services that should be protected under the defined authorization policies. This issue has been addressed in Istio versions 1.29.1, 1.28.5, and 1.27.8.

Affected Version(s)

istio >= 1.29.0-alpha.0, < 1.29.1 < 1.29.0-alpha.0, 1.29.1

istio >= 1.28.0-alpha.0, < 1.28.5 < 1.28.0-alpha.0, 1.28.5

istio < 1.27.8 < 1.27.8

References

https://github.com/istio/istio/security/advisories/GHSA-9...
x_refsource_CONFIRM
https://github.com/istio/istio/commit/004fd6921314a8e2293...
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CVSS V4

Score:
6.9
Severity:
MEDIUM
Confidentiality:
Low
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.