# CVE-2026-84303

## Summary

- **CVE ID:** CVE-2026-84303
- **Severity:** MEDIUM
- **CVSS Score:** 6.3 (CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N)
- **CWE:** CWE-178, CWE-863
- **Published:** Sep 1, 2026
- **Last Modified:** Sep 2, 2026

## Description

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.

## Affected Products

- grpc — grpc-go (< 1.83.1)

## References

- [CNA](https://github.com/grpc/grpc-go/security/advisories/GHSA-qc2q-p7wx-3px3)
- [CNA](https://github.com/grpc/grpc-go/pull/9332)
- [CNA](https://github.com/grpc/grpc-go/pull/9335)
- [CNA](https://github.com/grpc/grpc-go/commit/db9482836c298f234c896cf82ab68cafc78237f8)
- [CNA](https://github.com/grpc/grpc-go/commit/ebba6f3f1b206e2b4dc4d1d5a96d18430302c2fe)
- [CNA](https://github.com/grpc/grpc-go/releases/tag/v1.83.1)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.31%
- **EPSS Percentile:** 23.6

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._