CVE-2021-31920

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.3% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2021-05-27 · updated 2026-06-17
Weakness: CWE-706

Description

Istio before 1.8.6 and 1.9.x before 1.9.5 has a remotely exploitable vulnerability where an HTTP request path with multiple slashes or escaped slash characters (%2F or %5C) could potentially bypass an Istio authorization policy when path based authorization rules are used.

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-2021-005/
https://istio.io/latest/news/security/istio-security-2021-005/

Get alerted when CVE-2021-31920 or the next vulnerability affects your stack