gRPC-Go: xDS RBAC HTTP Filter bypass via mixed-case Header Matching and gRFC A41 validation evasion (CVE-2026-84303) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-84303

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

Answer in brief

CVE-2026-84303 records a Unknown severity vulnerability in gRPC-Go: xDS RBAC HTTP Filter bypass via mixed-case Header Matching and gRFC A41 validation evasion. The current sources do not mark it as known exploited. The current feed maps grpc/grpc-go (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 1, 2026Updated Sep 1, 2026Source checked Sep 1, 2026First seen by HOL Sep 1, 2026Material review Sep 1, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Not reported

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps grpc/grpc-go (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
grpc/grpc-gogeneric	< 1.83.1	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for grpc/grpc-go.
Review the reported fix. Monitor this advisory for an available fix and review any installs of the affected package.

Evidence timeline and material changes

Published upstream
Sep 1, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 1, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 1, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.