CVE-2026-84445

gRPC-Go is the Go language implementation of gRPC. Prior to 1.82.2 and 1.83.2, servers created with xds.NewGRPCServer() allow internal/transport/http2_server.go to accept an RPC containing neither the :authority header nor the Host header, while RouteAndProcess in internal/xds/server/routing.go assumes that an authority value exists and indexes the empty slice. A remote client that can complete transport connection establishment can trigger an index-out-of-bounds panic that is not recovered by the per-RPC goroutine and terminates the entire server process. In insecure or ordinary TLS deployments the request can be unauthenticated, while strict mTLS or ALTS deployments require valid transport credentials before the malformed RPC can reach the interceptor. This issue is fixed in versions 1.82.2 and 1.83.2.

gRPC-Go is the Go language implementation of gRPC. Prior to 1.82.2 and 1.83.2, servers created with xds.NewGRPCServer() allow internal/transport/http2_server.go to accept an RPC containing neither the :authority header nor the Host header, while RouteAndProcess in internal/xds/server/routing.go assumes that an authority value exists and indexes the empty slice. A remote client that can complete transport connection establishment can trigger an index-out-of-bounds panic that is not recovered by the per-RPC goroutine and terminates the entire server process. In insecure or ordinary TLS deployments the request can be unauthenticated, while strict mTLS or ALTS deployments require valid transport credentials before the malformed RPC can reach the interceptor. This issue is fixed in versions 1.82.2 and 1.83.2.

In google.golang.org/grpc, servers configured with xDS routing can panic when processing requests that lack both :authority and Host headers. The HTTP/2 transport layer accepted requests missing these headers, and the xDS server routing interceptor attempted to index the empty authority slice, causing an unhandled panic and terminating the server.

A vulnerability exists in gRPC-Go servers configured with `xds.NewGRPCServer()` where a crafted request missing both `:authority` and `Host` headers can cause a server panic, resulting in a Denial of Service (DoS). Servers built with `xds.NewGRPCServer` install an xDS routing interceptor on every RPC. This interceptor looks up the request’s `:authority` header to pick a virtual host. The HTTP/2 server transport previously accepted requests that had neither `:authority` nor `Host`. When this happened, the xDS routing interceptor attempted to access the first element of an empty slice of authorities, leading to an index out of bounds panic. Since the per-RPC goroutine does not recover from panics, the entire server process would terminate. This panic occurs in the interceptor pipeline, meaning the transport credentials handshake (TLS, mTLS, or ALTS) and HTTP/2 connection establishment must complete successfully before the crafted request can reach this logic. - Insecure/Standard TLS: If the server permits insecure (plaintext) connections or standard credentials (where client certs are not checked), any unauthenticated remote attacker can trigger the crash. - mTLS / ALTS: If strict transport-level authentication is enforced at the network edge or transport layer (e.g., requiring a valid client certificate), the attacker must possess valid transport credentials to initiate the stream and trigger the panic. ### Impact An attacker can cause a complete outage of the gRPC server by sending a request missing both `:authority` and `Host` headers, provided they can successfully establish a transport connection. ### Patches The issue has been addressed in `master` (and backported to `1.83.2` and `1.82.2`). The fix updates the HTTP/2 transport layer to reject requests missing both `:authority` and `Host` headers early, maintaining consistency with and other gRPC language implementations.