Auth bypass in Istio

CVE-2026-39350

Istio is an open platform to connect, manage, and secure microservices. In versions 1.25.0 through 1.27.8, 1.28.0 through 1.28.5, 1.29.0, and 1.29.1, the serviceAccounts and notServiceAccounts fields in AuthorizationPolicy incorrectly interpret dots (.) as a regular expression matcher. Because . is a valid character in a service account name, an AuthorizationPolicy ALLOW rule targeting a service account such as cert-manager.io also matches cert-manager-io, cert-managerXio, etc. A DENY rule targeting the same name fails to block those variants. Fixes are available in versions 1.29.2, 1.28.6, and 1.27.9.

Published · last modified .

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.002 (12.5th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 12th percentile — 12.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-39350: held from 0.002 to 0.002.

EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: +0.000

Affected products

  • Istio — versions >= 1.25.0, < < 1.27.9, >= 1.28.0, < 1.28.6, >= 1.29.0, < 1.29.2

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-39350?
CVE-2026-39350 is a medium-severity vulnerability in Istio, classified under Incorrect Regular Expression. CVSS score: 5.4/10. Published 2026-04-15.
How severe is CVE-2026-39350?
Medium severity. CVSS v3 base score is 5.4 out of 10.