CVE intelligence

CVE-2026-84303

Vulnerability intelligence

Published Sep 1, 2026Sources checked Oct 28, 2026

6.3MEDIUMCVSS out of 10

What this means

Review the available evidence

CVE-2026-84303 and is rated Medium severity with a CVSS score of 6.3. It is not in the current CISA KEV record we collected. That does not prove exploitation has not occurred.

What to do next

Remediation and response

Microsoft Security Response Center guidance

Vendor revision: Sep 8, 2026

See the Microsoft Security Update Guide for the update that applies to your product.

CISA KEVNot listedBased on the latest collected catalog

EPSS0.3%Estimated 30-day exploitation probability

Ransomware useNot markedCISA KEV ransomware field

Threat actors0Source-linked actor relationships

Overview

What is CVE-2026-84303?

gRPC-Go is the Go language implementation of gRPC. Prior to 1.83.1, the xDS RBAC HTTP filter in internal/xds/httpfilter/rbac/rbac.go does not lowercase header matcher names in normalizeHeaderMatcher even though incoming metadata keys are lowercase.

A DENY policy using a mixed-case name such as X-Role or User-Agent therefore does not match and fails open, allowing requests that should be rejected. The same case mismatch permits :Scheme or Grpc-Status to evade gRFC A41 validation and prevents Host from being rewritten to :authority.

This issue is fixed in version 1.83.1.

Source: NVD