Skip to content

Cap webhook middleware request body at 1 MB #5192

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
JAORMX wants to merge 1 commit into
base: main
Choose a base branch
from
Open

Cap webhook middleware request body at 1 MB #5192

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
10 changes: 9 additions & 1 deletion pkg/webhook/mutating/middleware.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@ import (
"bytes"
"context"
"encoding/json"
"errors"
"fmt"
"io"
"log/slog"
Expand Down Expand Up @@ -88,9 +89,16 @@ func createMutatingHandler(executors []clientExecutor, serverName, transport str
return
}

// Read the request body to get the raw MCP request.
// Read the request body to get the raw MCP request, capped at MaxRequestSize
// to prevent unbounded memory consumption from oversized inbound requests.
r.Body = http.MaxBytesReader(w, r.Body, webhook.MaxRequestSize)
bodyBytes, err := io.ReadAll(r.Body)
if err != nil {
var maxErr *http.MaxBytesError
if errors.As(err, &maxErr) {
sendErrorResponse(w, http.StatusRequestEntityTooLarge, "Request body exceeds maximum size", parsedMCP.ID)
return
}
sendErrorResponse(w, http.StatusInternalServerError, "Failed to read request body", parsedMCP.ID)
return
}
Expand Down
75 changes: 75 additions & 0 deletions pkg/webhook/mutating/middleware_test.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -405,6 +405,81 @@ func TestMutatingMiddleware_SkipNonMCPRequests(t *testing.T) {
assert.Equal(t, http.StatusOK, rr.Code)
}

// makeJSONBodyOfSize builds a syntactically-valid JSON body of exactly `size`
// bytes by padding the value of a "data" field with ASCII characters. The
// resulting bytes are valid JSON-RPC for use as an MCP request body.
func makeJSONBodyOfSize(tb testing.TB, size int) []byte {
tb.Helper()
const envelope = `{"jsonrpc":"2.0","method":"tools/call","id":1,"data":""}`
if size < len(envelope) {
tb.Fatalf("requested size %d is smaller than minimum envelope size %d", size, len(envelope))
}
padding := bytes.Repeat([]byte("a"), size-len(envelope))
body := []byte(`{"jsonrpc":"2.0","method":"tools/call","id":1,"data":"`)
body = append(body, padding...)
body = append(body, []byte(`"}`)...)
if len(body) != size {
tb.Fatalf("constructed body length %d != requested size %d", len(body), size)
}
return body
}

func TestMutatingMiddleware_RequestBodySizeLimit(t *testing.T) {
t.Parallel()

t.Run("body exceeding MaxRequestSize returns 413", func(t *testing.T) {
t.Parallel()

cfg := makeConfig(closedServerURL, webhook.FailurePolicyIgnore)
mw := createMutatingHandler(makeExecutors(t, []webhook.Config{cfg}), "srv", "stdio")

body := makeJSONBodyOfSize(t, webhook.MaxRequestSize+1)
req := httptest.NewRequest(http.MethodPost, "/", bytes.NewReader(body))
ctx := context.WithValue(req.Context(), mcp.MCPRequestContextKey, &mcp.ParsedMCPRequest{Method: "tools/call", ID: 1})
req = req.WithContext(ctx)

var nextCalled bool
nextHandler := http.HandlerFunc(func(_ http.ResponseWriter, _ *http.Request) { nextCalled = true })

rr := httptest.NewRecorder()
mw(nextHandler).ServeHTTP(rr, req)

assert.False(t, nextCalled, "next must not be called for oversized requests")
assert.Equal(t, http.StatusRequestEntityTooLarge, rr.Code)

var errResp map[string]interface{}
require.NoError(t, json.Unmarshal(rr.Body.Bytes(), &errResp))
errObj, ok := errResp["Error"].(map[string]interface{})
require.True(t, ok)
assert.Equal(t, float64(http.StatusRequestEntityTooLarge), errObj["code"])
assert.Equal(t, "Request body exceeds maximum size", errObj["message"])
})

t.Run("body at MaxRequestSize boundary is accepted", func(t *testing.T) {
t.Parallel()

// Use FailurePolicyIgnore against a closed port: the outbound webhook
// call fails and is ignored per fail-open, so next is invoked. This
// isolates the test from depending on a working webhook server.
cfg := makeConfig(closedServerURL, webhook.FailurePolicyIgnore)
mw := createMutatingHandler(makeExecutors(t, []webhook.Config{cfg}), "srv", "stdio")

body := makeJSONBodyOfSize(t, webhook.MaxRequestSize)
req := httptest.NewRequest(http.MethodPost, "/", bytes.NewReader(body))
ctx := context.WithValue(req.Context(), mcp.MCPRequestContextKey, &mcp.ParsedMCPRequest{Method: "tools/call", ID: 1})
req = req.WithContext(ctx)

var nextCalled bool
nextHandler := http.HandlerFunc(func(_ http.ResponseWriter, _ *http.Request) { nextCalled = true })

rr := httptest.NewRecorder()
mw(nextHandler).ServeHTTP(rr, req)

assert.True(t, nextCalled, "next should be called for boundary-size body (fail-open ignores webhook error)")
assert.Equal(t, http.StatusOK, rr.Code)
})
}

func TestMiddlewareParams_Validate(t *testing.T) {
t.Parallel()
tests := []struct {
Expand Down
5 changes: 5 additions & 0 deletions pkg/webhook/types.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,11 @@ const MinTimeout = 1 * time.Second
// MaxResponseSize is the maximum allowed size in bytes for webhook responses (1 MB).
const MaxResponseSize = 1 << 20

// MaxRequestSize is the maximum allowed size in bytes for inbound webhook
// middleware request bodies (1 MB). Requests exceeding this size are
// rejected with HTTP 413 before the body is buffered or forwarded.
const MaxRequestSize = 1 << 20

// Type indicates whether a webhook is validating or mutating.
type Type string

Expand Down
10 changes: 9 additions & 1 deletion pkg/webhook/validating/middleware.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@ import (
"bytes"
"context"
"encoding/json"
"errors"
"fmt"
"io"
"log/slog"
Expand Down Expand Up @@ -97,9 +98,16 @@ func createValidatingHandler(executors []clientExecutor, serverName, transport s
return
}

// Read the request body to get the raw MCP request
// Read the request body to get the raw MCP request, capped at MaxRequestSize
// to prevent unbounded memory consumption from oversized inbound requests.
r.Body = http.MaxBytesReader(w, r.Body, webhook.MaxRequestSize)
bodyBytes, err := io.ReadAll(r.Body)
if err != nil {
var maxErr *http.MaxBytesError
if errors.As(err, &maxErr) {
sendErrorResponse(w, http.StatusRequestEntityTooLarge, "Request body exceeds maximum size", parsedMCP.ID)
return
}
sendErrorResponse(w, http.StatusInternalServerError, "Failed to read request body", parsedMCP.ID)
return
}
Expand Down
96 changes: 96 additions & 0 deletions pkg/webhook/validating/middleware_test.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -270,6 +270,102 @@ func TestValidatingMiddleware(t *testing.T) {
})
}

// makeJSONBodyOfSize builds a syntactically-valid JSON body of exactly `size`
// bytes by padding the value of a "data" field with ASCII characters. The
// resulting bytes are valid JSON-RPC for use as an MCP request body.
func makeJSONBodyOfSize(tb testing.TB, size int) []byte {
tb.Helper()
// Envelope structure: {"jsonrpc":"2.0","method":"tools/call","id":1,"data":"<padding>"}
const envelope = `{"jsonrpc":"2.0","method":"tools/call","id":1,"data":""}`
if size < len(envelope) {
tb.Fatalf("requested size %d is smaller than minimum envelope size %d", size, len(envelope))
}
padding := bytes.Repeat([]byte("a"), size-len(envelope))
body := []byte(`{"jsonrpc":"2.0","method":"tools/call","id":1,"data":"`)
body = append(body, padding...)
body = append(body, []byte(`"}`)...)
if len(body) != size {
tb.Fatalf("constructed body length %d != requested size %d", len(body), size)
}
return body
}

func TestValidatingMiddleware_RequestBodySizeLimit(t *testing.T) {
t.Parallel()

t.Run("body exceeding MaxRequestSize returns 413", func(t *testing.T) {
t.Parallel()

// Use fail-open so that even if the middleware reached the webhook call
// (it must NOT, since the size check fires first), the test would still
// be unambiguous about the size rejection vs. a downstream error.
cfg := webhook.Config{
Name: "test-webhook",
URL: closedServerURL,
Timeout: webhook.DefaultTimeout,
FailurePolicy: webhook.FailurePolicyIgnore,
TLSConfig: &webhook.TLSConfig{InsecureSkipVerify: true},
}
client, err := webhook.NewClient(cfg, webhook.TypeValidating, nil)
require.NoError(t, err)
mw := createValidatingHandler([]clientExecutor{{client: client, config: cfg}}, "srv", "stdio")

body := makeJSONBodyOfSize(t, webhook.MaxRequestSize+1)
req := httptest.NewRequest(http.MethodPost, "/", bytes.NewReader(body))
ctx := context.WithValue(req.Context(), mcp.MCPRequestContextKey, &mcp.ParsedMCPRequest{Method: "tools/call", ID: 1})
req = req.WithContext(ctx)

var nextCalled bool
nextHandler := http.HandlerFunc(func(_ http.ResponseWriter, _ *http.Request) { nextCalled = true })

rr := httptest.NewRecorder()
mw(nextHandler).ServeHTTP(rr, req)

assert.False(t, nextCalled, "next must not be called for oversized requests")
assert.Equal(t, http.StatusRequestEntityTooLarge, rr.Code)

// The error response is a JSON-RPC envelope.
var errResp map[string]interface{}
require.NoError(t, json.Unmarshal(rr.Body.Bytes(), &errResp))
errObj, ok := errResp["Error"].(map[string]interface{})
require.True(t, ok)
assert.Equal(t, float64(http.StatusRequestEntityTooLarge), errObj["code"])
assert.Equal(t, "Request body exceeds maximum size", errObj["message"])
})

t.Run("body at MaxRequestSize boundary is accepted", func(t *testing.T) {
t.Parallel()

// Point at a closed port with FailurePolicyIgnore so that the outbound
// webhook call fails and is ignored per fail-open. This isolates the
// test from depending on a working webhook server.
cfg := webhook.Config{
Name: "test-webhook",
URL: closedServerURL,
Timeout: webhook.DefaultTimeout,
FailurePolicy: webhook.FailurePolicyIgnore,
TLSConfig: &webhook.TLSConfig{InsecureSkipVerify: true},
}
client, err := webhook.NewClient(cfg, webhook.TypeValidating, nil)
require.NoError(t, err)
mw := createValidatingHandler([]clientExecutor{{client: client, config: cfg}}, "srv", "stdio")

body := makeJSONBodyOfSize(t, webhook.MaxRequestSize)
req := httptest.NewRequest(http.MethodPost, "/", bytes.NewReader(body))
ctx := context.WithValue(req.Context(), mcp.MCPRequestContextKey, &mcp.ParsedMCPRequest{Method: "tools/call", ID: 1})
req = req.WithContext(ctx)

var nextCalled bool
nextHandler := http.HandlerFunc(func(_ http.ResponseWriter, _ *http.Request) { nextCalled = true })

rr := httptest.NewRecorder()
mw(nextHandler).ServeHTTP(rr, req)

assert.True(t, nextCalled, "next should be called for boundary-size body (fail-open ignores webhook error)")
assert.Equal(t, http.StatusOK, rr.Code)
})
}

func TestMiddlewareParams_Validate(t *testing.T) {
t.Parallel()
tests := []struct {
Expand Down
Loading