Is CVE-2026-31838 in the CISA KEV catalog?

No. CVE-2026-31838 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-31838?

CVE-2026-31838 has a CVSS v3 base score of 5.3 (MEDIUM).

What is the EPSS score for CVE-2026-31838?

CVE-2026-31838 has an EPSS score of 0.21% (12th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-31838?

Upgrade istio to 1.29.1 or later.

CVE & CISA-KEV Catalog

CVE-2026-31838

MEDIUM

5.3

CVSS v3

NVD

Description

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.

CWE-863Incorrect Authorization

How to fix

Remediation Available

istioNVD

Affected:>= 1.29.0, < 1.29.1Fixed in:1.29.1CVE-2026-31838derived from NVD

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityLow

IntegrityNone

AvailabilityNone

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Exploit Intelligence

0.21%probability of exploitation in 30 days

12thpercentile

Low risk: more likely to be exploited than 12% of all known CVEs.

References

Vendor Advisory1

github.com

Other references1

github.com

Related Vulnerabilities

Other CWE-863 (Incorrect Authorization) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2023-22518	Critical	9.8	100%	KEV + Ransom	Fix
CVE-2023-38035	Critical	9.8	100%	KEV + Ransom	-
CVE-2022-46169	Critical	9.8	100%	KEV	Fix
CVE-2025-29927	Critical	9.1	100%	-	Fix
CVE-2024-38856	Critical	9.8	99%	KEV	Fix
CVE-2020-36289	Medium	5.3	99%	-	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-04-07.