fix: Handle invalid signatures correctly, move signature checks earli…

…er to avoid storing request body.

adapters/flashbots/signature.go

@@ -16,7 +16,7 @@ var (
 	ErrInvalidSignature = errors.New("invalid signature provided")
 )
 
-func ParseSignature(header string, body []byte) (string, error) {
+func ParseSignature(header string, body []byte) (signingAddress string, err error) {
 	if header == "" {
 		return "", ErrNoSignature
 	}
@@ -29,7 +29,7 @@ func ParseSignature(header string, body []byte) (string, error) {
 	return VerifySignature(body, splitSig[0], splitSig[1])
 }
 
-func VerifySignature(body []byte, signingAddressStr, signatureStr string) (string, error) {
+func VerifySignature(body []byte, signingAddressStr, signatureStr string) (signingAddress string, err error) {
 	signature, err := hexutil.Decode(signatureStr)
 	if err != nil || len(signature) == 0 {
 		return "", fmt.Errorf("%w: %w", ErrInvalidSignature, err)

server/request_handler.go

@@ -148,9 +148,11 @@ func (r *RpcRequestHandler) processRequest(client RPCProxyClient, jsonReq *types
 	// Handle single request
 	rpcReq := NewRpcRequest(r.logger, client, jsonReq, r.relaySigningKey, r.relayUrl, origin, referer, isWhitehatBundleCollection, whitehatBundleId, entry, urlParams, r.chainID, r.rpcCache)
 
-	if r.req.Header.Get("X-Flashbots-Signature") != "" {
-		rpcReq.flashbotsSignature = r.req.Header.Get("X-Flashbots-Signature")
-		rpcReq.flashbotsSignatureBody = body
+	if err := rpcReq.CheckFlashbotsSignature(r.req.Header.Get("X-Flashbots-Signature"), body); err != nil {
+		r.logger.Warn("[processRequest] CheckFlashbotsSignature", "error", err)
+		rpcReq.writeRpcError(err.Error(), types.JsonRpcInvalidRequest)
+		r._writeRpcResponse(rpcReq.jsonRes)
+		return
 	}
 	res := rpcReq.ProcessRequest()
 	// Write response

server/request_intercepts.go

@@ -1,11 +1,9 @@
 package server
 
 import (
-	"errors"
 	"fmt"
 	"strings"
 
-	"github.com/flashbots/rpc-endpoint/adapters/flashbots"
 	"github.com/flashbots/rpc-endpoint/types"
 )
 
@@ -154,8 +152,7 @@ func (r *RpcRequest) intercept_eth_call_to_FlashRPC_Contract() (requestFinished
 }
 
 func (r *RpcRequest) intercept_signed_eth_getTransactionCount() (requestFinished bool) {
-	signingAddress, err := flashbots.ParseSignature(r.flashbotsSignature, r.flashbotsSignatureBody)
-	if errors.Is(err, flashbots.ErrNoSignature) {
+	if r.flashbotsSigningAddress == "" {
 		r.logger.Info("[eth_getTransactionCount] No signature found")
 		return false
 	}
@@ -177,8 +174,8 @@ func (r *RpcRequest) intercept_signed_eth_getTransactionCount() (requestFinished
 		return false
 	}
 	addr = strings.ToLower(addr)
-	if addr != strings.ToLower(signingAddress) {
-		r.logger.Info("[eth_getTransactionCount] address mismatch", "addr", addr, "signingAddress", signingAddress)
+	if addr != strings.ToLower(r.flashbotsSigningAddress) {
+		r.logger.Info("[eth_getTransactionCount] address mismatch", "addr", addr, "signingAddress", r.flashbotsSigningAddress)
 		return false
 	}
 

server/request_processor.go

@@ -13,6 +13,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/flashbots/rpc-endpoint/adapters/flashbots"
 	"github.com/flashbots/rpc-endpoint/application"
 	"github.com/flashbots/rpc-endpoint/database"
 
@@ -42,8 +43,7 @@ type RpcRequest struct {
 	urlParams                  URLParameters
 	chainID                    []byte
 	rpcCache                   *application.RpcCache
-	flashbotsSignature         string
-	flashbotsSignatureBody     []byte
+	flashbotsSigningAddress    string
 }
 
 func NewRpcRequest(
@@ -501,3 +501,23 @@ func (r *RpcRequest) writeRpcResult(result interface{}) {
 		Result:  resBytes,
 	}
 }
+
+// CheckFlashbotsSignature parses and validates the Flashbots signature if present,
+// returning an error if the signature is invalid.  If the signature is present and valid
+// the signing address is stored in the request.
+func (r *RpcRequest) CheckFlashbotsSignature(signature string, body []byte) error {
+	// Most requests don't have a signature, so avoid parsing it if it's empty
+	if signature == "" {
+		return nil
+	}
+	signingAddress, err := flashbots.ParseSignature(signature, body)
+	if err != nil {
+		if errors.Is(err, flashbots.ErrNoSignature) {
+			return nil
+		} else {
+			return err
+		}
+	}
+	r.flashbotsSigningAddress = signingAddress
+	return nil
+}