🚨 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.
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GitHub
xds/rbac: lowercase header matcher names before matching (#9332) · grpc/grpc-go@db94828
The RBAC filter passes the name of a header matcher to the matching
engine unchanged. The metadata that the engine matches against always
has lowercase keys. A name that contains an uppercase chara...
September 1, 2026 8
