CVE-2021-39156: Fragments in Path May Lead to Authorization Policy Bypass

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-08-24 · updated 2026-06-17
Weakness: CWE-863

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. Istio 1.11.0, 1.10.3 and below, and 1.9.7 and below contain a remotely exploitable vulnerability where an HTTP request with `#fragment` in the path may bypass Istio’s URI path based authorization policies. 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 the path.

Affected products

istio: before 1.9.8; from 1.10.0 before 1.10.3; from 1.11.0 before 1.11.1 — fixed in 1.10.3, 1.11.1, 1.9.8

How to fix

Upgrade to a fixed version: istio 1.10.3, 1.11.1, 1.9.8. Check the vendor advisory for mitigations.

References

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