CVE-2021-31921

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.5% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2021-06-02 · updated 2026-06-17
Weakness: CWE-862

Description

Istio before 1.8.6 and 1.9.x before 1.9.5 contains a remotely exploitable vulnerability where an external client can access unexpected services in the cluster, bypassing authorization checks, when a gateway is configured with AUTO_PASSTHROUGH routing configuration.

Affected products

istio: before 1.8.6; from 1.9.0 before 1.9.5 — fixed in 1.8.6, 1.9.5

How to fix

Upgrade to a fixed version: istio 1.8.6, 1.9.5. Check the vendor advisory for mitigations.

References

https://istio.io/latest/news/security/istio-security-2021-006/
https://istio.io/latest/news/security/istio-security-2021-006/

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