Auth bypass in Istio
CVE-2026-31838
Istio is an open platform to connect, manage, and secure microservices. Prior to 1.29.1, 1.28.5, and 1.27.8, a vulnerability in Envoy RBAC header matching could allow authorization policy bypass when policies rely on HTTP headers that may contain multiple values. An attacker could craft requests with multiple header values in a way that causes Envoy to evaluate the header differently than intended, potentially bypassing authorization checks. This may allow unauthorized requests to reach protected services when policies depend on such header-based matching conditions. This vulnerability is fixed in 1.29.1, 1.28.5, and 1.27.8.
Vulnerability class: Broken Access Control
EPSS: 0.002 (12.0th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N.
Affected products
- Istio — versions >= 1.29.0-alpha.0, < 1.29.1, >= 1.28.0-alpha.0, < 1.28.5, < 1.27.8
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Vendor Advisory)
- security-advisories@github.com (x_refsource_MISC)
Frequently asked questions
- What is CVE-2026-31838?
- CVE-2026-31838 is a medium-severity vulnerability in Istio, classified under Incorrect Authorization. CVSS score: 5.3/10. Published 2026-03-10.
- How severe is CVE-2026-31838?
- Medium severity. CVSS v3 base score is 5.3 out of 10.