# CVE-2026-84303: gRPC-Go xDS RBAC HTTP filter bypass via case-sensitive header matching

Source: https://junglewise.ai/threats/cve-2026-84303-grpc-go-xds-rbac-http-filter-bypass-via-case-sensitive-header  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-01. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-84303 · Severity: medium · CVSS 4 · Published 2026-09-01

gRPC-Go is a widely-used remote procedure call framework that includes authorization policy enforcement through the xDS RBAC HTTP filter. The vulnerability allows attackers to bypass security policies by using mixed-case header names that fail to match case-sensitive policy definitions, causing restrictive rules to fail open and allow prohibited traffic. Additionally, safety guards against reserved gRPC headers can be evaded through case variations.

Technologies: [google.golang.org/grpc (Go)](https://junglewise.ai/threats/technologies/google-golang-org-grpc). Vendors: [Go](https://junglewise.ai/threats/vendors/go).

## Quick answers

**Is CVE-2026-84303 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-84303 being exploited in the wild.

**How severe is CVE-2026-84303?** Medium severity, with a CVSS score of 4, published 1 September 2026.

**Which products and versions are affected?** google.golang.org/grpc (Go) <= 1.83.0, SEMVER:introduced=0,fixed=1.83.1.

**Is there a fix for CVE-2026-84303?** Yes. google.golang.org/grpc (Go): upgrade to 1.83.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-84303 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-84303?** Check whether you run google.golang.org/grpc (Go) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- google.golang.org/grpc (Go): upgrade to 1.83.1 or later

  ```sh
  go get google.golang.org/grpc@v1.83.1
  ```


## Technical details

The vulnerability stems from improper case-sensitivity handling in two areas of the xDS RBAC HTTP filter: (1) policy matching logic that unconditionally lowercases incoming metadata keys but fails to normalize policy-defined header matchers, leading to non-matches when policies reference headers like "X-Role" but requests arrive with "x-role"; and (2) validation logic that case-sensitively checks for gRPC-reserved header prefixes (gRFC A41), allowing attackers to bypass restrictions using variants like "Grpc-Status". The attack requires network access and no authentication; an attacker can exploit this by crafting requests with mixed-case headers that evade security policies. The impact is limited to authorization bypass (no direct data exposure or availability impact). The fix is available in grpc-go version 1.83.1 and later.

## Affected products

- Google gRPC-Go <= 1.83.0

## Identifiers

- CVE-2026-84303
- GHSA-qc2q-p7wx-3px3
- GO-2026-6441

## Timeline

- 2026-08-19: disclosed
- 2026-09-01: patched: Fixed in version 1.83.1
- 2026-09-08: advisory: GitHub advisory GHSA-qc2q-p7wx-3px3 published

## References

- [https://api.github.com/users/alimony](https://api.github.com/users/alimony)
- [https://github.com/alimony](https://github.com/alimony)
- [https://api.github.com/users/alimony/gists%7B/gist_id%7D](https://api.github.com/users/alimony/gists%7B/gist_id%7D)
- [https://api.github.com/users/alimony/repos](https://api.github.com/users/alimony/repos)
- [https://avatars.githubusercontent.com/u/331091?v=4](https://avatars.githubusercontent.com/u/331091?v=4)
- [https://api.github.com/users/alimony/events%7B/privacy%7D](https://api.github.com/users/alimony/events%7B/privacy%7D)

## Related threats

- [gRPC-Go xDS server denial of service via missing headers](https://junglewise.ai/threats/cve-2026-84445-grpc-go-xds-server-denial-of-service-via-missing-headers)
- [gRPC-Go heap memory exhaustion via HTTP/2 DATA frame fragmentation](https://junglewise.ai/threats/cve-2026-84304-grpc-go-heap-memory-exhaustion-via-http-2-data-frame)
- [GO-2026-6061 - Vulnerabilities in the xDS RBAC authorization engine and the HTTP/2 transport server implementation in…](https://junglewise.ai/threats/go-2026-6061-vulnerabilities-in-the-xds-rbac-authorization-engine-and-2c07d92a)
- [gRPC-Go auth bypass and DoS in xDS RBAC and HTTP/2 transport](https://junglewise.ai/threats/grpc-go-auth-bypass-and-dos-in-xds-rbac-and-http-2-transport-878951d5)
- [gRPC gRPC-Go authorization bypass in HTTP/2 path validation](https://junglewise.ai/threats/cve-2026-33186-grpc-grpc-go-authorization-bypass-in-http-2-path-validation)