| Package | Affected versions | Patched versions |
|---|---|---|
| google.golang.org/grpc | < 1.79.3 | 1.79.3 |
| grpc | < 1.79.3 | 1.79.3 |
What kind of vulnerability is it? Who is impacted?
It is an Authorization Bypass resulting from Improper Input Validation of the HTTP/2 :path pseudo-header.
The gRPC-Go server was too lenient in its routing logic, accepting requests where the :path omitted the mandatory leading slash (e.g., Service/Method instead of /Service/Method). While the server successfully routed these requests to the correct handler, authorization interceptors (including the official grpc/authz package) evaluated the raw, non-canonical path string. Consequently, "deny" rules defined using canonical paths (starting with /) failed to match the incoming request, allowing it to bypass the policy if a fallback "allow" rule was present.
Who is impacted? This affects gRPC-Go servers that meet both of the following criteria:
google.golang.org/grpc/authz or custom interceptors relying on info.FullMethod or grpc.Method(ctx).The vulnerability is exploitable by an attacker who can send raw HTTP/2 frames with malformed headers directly to the gRPC server.
:pathHas the problem been patched? What versions should users upgrade to?
Yes, the issue has been patched. The fix ensures that any request with a :path that does not start with a leading slash is immediately rejected with a codes.Unimplemented error, preventing it from reaching authorization interceptors or handlers with a non-canonical path string.
Users should upgrade to the following versions (or newer):
It is recommended that all users employing path-based authorization (especially grpc/authz) upgrade as soon as the patch is available in a tagged release.
Is there a way for users to fix or remediate the vulnerability without upgrading?
While upgrading is the most secure and recommended path, users can mitigate the vulnerability using one of the following methods:
Add an "outermost" interceptor to your server that validates the path before any other authorization logic runs:
func pathValidationInterceptor(ctx context.Context, req any, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (any, error) {
if info.FullMethod == "" || info.FullMethod[0] != '/' {
return nil, status.Errorf(codes.Unimplemented, "malformed method name")
}
return handler(ctx, req)
}
// Ensure this is the FIRST interceptor in your chain
s := grpc.NewServer(
grpc.ChainUnaryInterceptor(pathValidationInterceptor, authzInterceptor),
)
If your gRPC server is behind a reverse proxy or load balancer (such as Envoy, NGINX, or an L7 Cloud Load Balancer), ensure it is configured to enforce strict HTTP/2 compliance for pseudo-headers and reject or normalize requests where the :path header does not start with a leading slash.
Switch to a "default deny" posture in your authorization policies (explicitly listing all allowed paths and denying everything else) to reduce the risk of bypasses via malformed inputs.
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