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all: use case-sensitive JSON unmarshaling (#807)

Browse source 
As reported in
https://github.com/modelcontextprotocol/go-sdk/issues/805, case
insensitive unmarshaling can pose security issues. This change adjusts
all non-test and non-example unmarshaling to use a case sensitive mode.

This introduces a new external dependency
`github.com/segmentio/encoding`.
This commit is contained in:
Maciej Kisiel 2026-02-18 16:38:36 +01:00 • committed by GitHub
commit 7b8d81c264
No known key found for this signature in database
GPG key ID: B5690EEEBB952194
9 changed files with 134 additions and 25 deletions
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3
mcp/client.go
View file

@ -6,7 +6,6 @@ package mcp
import (
"context"
"encoding/json"
"errors"
"fmt"
"iter"
@ -18,7 +17,7 @@ import (
"time"
"github.com/google/jsonschema-go/jsonschema"
"github.com/modelcontextprotocol/go-sdk/internal/json"
"github.com/modelcontextprotocol/go-sdk/internal/jsonrpc2"
"github.com/modelcontextprotocol/go-sdk/jsonrpc"
)

8
mcp/content.go
View file

@ -10,6 +10,8 @@ package mcp
import (
"encoding/json"
"fmt"
internaljson "github.com/modelcontextprotocol/go-sdk/internal/json"
)
// A Content is a [TextContent], [ImageContent], [AudioContent],
@ -248,7 +250,7 @@ func (c *ToolResultContent) MarshalJSON() ([]byte, error) {
return nil, err
}
var w wireContent
if err := json.Unmarshal(data, &w); err != nil {
if err := internaljson.Unmarshal(data, &w); err != nil {
return nil, err
}
contentWire = append(contentWire, &w)
@ -328,11 +330,11 @@ func unmarshalContent(raw json.RawMessage, allow map[string]bool) ([]Content, er
}
// Try array first, then fall back to single object.
var wires []*wireContent
if err := json.Unmarshal(raw, &wires); err == nil {
if err := internaljson.Unmarshal(raw, &wires); err == nil {
return contentsFromWire(wires, allow)
}
var wire wireContent
if err := json.Unmarshal(raw, &wire); err != nil {
if err := internaljson.Unmarshal(raw, &wire); err != nil {
return nil, err
}
c, err := contentFromWire(&wire, allow)

16
mcp/protocol.go
View file

@ -14,6 +14,8 @@ import (
"encoding/json"
"fmt"
"maps"
internaljson "github.com/modelcontextprotocol/go-sdk/internal/json"
)
// Optional annotations for the client. The client can use annotations to inform
@ -141,7 +143,7 @@ func (x *CallToolResult) UnmarshalJSON(data []byte) error {
res
Content []*wireContent `json:"content"`
}
if err := json.Unmarshal(data, &wire); err != nil {
if err := internaljson.Unmarshal(data, &wire); err != nil {
return err
}
var err error
@ -315,7 +317,7 @@ type CompleteReference struct {
func (r *CompleteReference) UnmarshalJSON(data []byte) error {
type wireCompleteReference CompleteReference // for naive unmarshaling
var r2 wireCompleteReference
if err := json.Unmarshal(data, &r2); err != nil {
if err := internaljson.Unmarshal(data, &r2); err != nil {
return err
}
switch r2.Type {
@ -502,7 +504,7 @@ func (m *SamplingMessageV2) UnmarshalJSON(data []byte) error {
msg
Content json.RawMessage `json:"content"`
}
if err := json.Unmarshal(data, &wire); err != nil {
if err := internaljson.Unmarshal(data, &wire); err != nil {
return err
}
var err error
@ -542,7 +544,7 @@ func (r *CreateMessageResult) UnmarshalJSON(data []byte) error {
result
Content *wireContent `json:"content"`
}
if err := json.Unmarshal(data, &wire); err != nil {
if err := internaljson.Unmarshal(data, &wire); err != nil {
return err
}
var err error
@ -605,7 +607,7 @@ func (r *CreateMessageWithToolsResult) UnmarshalJSON(data []byte) error {
result
Content json.RawMessage `json:"content"`
}
if err := json.Unmarshal(data, &wire); err != nil {
if err := internaljson.Unmarshal(data, &wire); err != nil {
return err
}
var err error
@ -1056,7 +1058,7 @@ func (m *PromptMessage) UnmarshalJSON(data []byte) error {
msg
Content *wireContent `json:"content"`
}
if err := json.Unmarshal(data, &wire); err != nil {
if err := internaljson.Unmarshal(data, &wire); err != nil {
return err
}
var err error
@ -1253,7 +1255,7 @@ func (m *SamplingMessage) UnmarshalJSON(data []byte) error {
msg
Content *wireContent `json:"content"`
}
if err := json.Unmarshal(data, &wire); err != nil {
if err := internaljson.Unmarshal(data, &wire); err != nil {
return err
}
// Allow text, image, audio, tool_use, and tool_result in sampling messages

5
mcp/server.go
View file

@ -25,6 +25,7 @@ import (
"time"
"github.com/google/jsonschema-go/jsonschema"
internaljson "github.com/modelcontextprotocol/go-sdk/internal/json"
"github.com/modelcontextprotocol/go-sdk/internal/jsonrpc2"
"github.com/modelcontextprotocol/go-sdk/internal/util"
"github.com/modelcontextprotocol/go-sdk/jsonrpc"
@ -327,7 +328,7 @@ func toolForErr[In, Out any](t *Tool, h ToolHandlerFor[In, Out], cache *SchemaCa
// Unmarshal and validate args.
var in In
if input != nil {
if err := json.Unmarshal(input, &in); err != nil {
if err := internaljson.Unmarshal(input, &in); err != nil {
return nil, fmt.Errorf("%w: %v", jsonrpc2.ErrInvalidParams, err)
}
}
@ -1371,7 +1372,7 @@ func initializeMethodInfo() methodInfo {
info.unmarshalParams = func(m json.RawMessage) (Params, error) {
var params *initializeParamsV2
if m != nil {
if err := json.Unmarshal(m, &params); err != nil {
if err := internaljson.Unmarshal(m, &params); err != nil {
return nil, fmt.Errorf("unmarshaling %q into a %T: %w", m, params, err)
}
}

3
mcp/shared.go
View file

@ -23,6 +23,7 @@ import (
"time"
"github.com/modelcontextprotocol/go-sdk/auth"
internaljson "github.com/modelcontextprotocol/go-sdk/internal/json"
"github.com/modelcontextprotocol/go-sdk/internal/jsonrpc2"
"github.com/modelcontextprotocol/go-sdk/jsonrpc"
)
@ -283,7 +284,7 @@ func newMethodInfo[P paramsPtr[T], R Result, T any](flags methodFlags) methodInf
unmarshalParams: func(m json.RawMessage) (Params, error) {
var p P
if m != nil {
if err := json.Unmarshal(m, &p); err != nil {
if err := internaljson.Unmarshal(m, &p); err != nil {
return nil, fmt.Errorf("unmarshaling %q into a %T: %w", m, p, err)
}
}

3
mcp/streamable.go
View file

@ -30,6 +30,7 @@ import (
"time"
"github.com/modelcontextprotocol/go-sdk/auth"
internaljson "github.com/modelcontextprotocol/go-sdk/internal/json"
"github.com/modelcontextprotocol/go-sdk/internal/jsonrpc2"
"github.com/modelcontextprotocol/go-sdk/internal/mcpgodebug"
"github.com/modelcontextprotocol/go-sdk/internal/util"
@ -1105,7 +1106,7 @@ func (c *streamableServerConn) servePOST(w http.ResponseWriter, req *http.Reques
isInitialize = true
// Extract the protocol version from InitializeParams.
var params InitializeParams
if err := json.Unmarshal(jreq.Params, &params); err == nil {
if err := internaljson.Unmarshal(jreq.Params, &params); err == nil {
initializeProtocolVersion = params.ProtocolVersion
}
}

3
mcp/tool.go
View file

@ -11,6 +11,7 @@ import (
"strings"
"github.com/google/jsonschema-go/jsonschema"
internaljson "github.com/modelcontextprotocol/go-sdk/internal/json"
)
// A ToolHandler handles a call to tools/call.
@ -83,7 +84,7 @@ func applySchema(data json.RawMessage, resolved *jsonschema.Resolved) (json.RawM
if resolved != nil {
v := make(map[string]any)
if len(data) > 0 {
if err := json.Unmarshal(data, &v); err != nil {
if err := internaljson.Unmarshal(data, &v); err != nil {
return nil, fmt.Errorf("unmarshaling arguments: %w", err)
}
}

5
mcp/transport.go
View file

@ -15,6 +15,7 @@ import (
"os"
"sync"
internaljson "github.com/modelcontextprotocol/go-sdk/internal/json"
"github.com/modelcontextprotocol/go-sdk/internal/jsonrpc2"
"github.com/modelcontextprotocol/go-sdk/internal/xcontext"
"github.com/modelcontextprotocol/go-sdk/jsonrpc"
@ -193,7 +194,7 @@ type canceller struct {
func (c *canceller) Preempt(ctx context.Context, req *jsonrpc.Request) (result any, err error) {
if req.Method == notificationCancelled {
var params CancelledParams
if err := json.Unmarshal(req.Params, &params); err != nil {
if err := internaljson.Unmarshal(req.Params, &params); err != nil {
return nil, err
}
id, err := jsonrpc2.MakeID(params.RequestID)
@ -569,7 +570,7 @@ func (t *ioConn) Read(ctx context.Context) (jsonrpc.Message, error) {
func readBatch(data []byte) (msgs []jsonrpc.Message, isBatch bool, _ error) {
// Try to read an array of messages first.
var rawBatch []json.RawMessage
if err := json.Unmarshal(data, &rawBatch); err == nil {
if err := internaljson.Unmarshal(data, &rawBatch); err == nil {
if len(rawBatch) == 0 {
return nil, true, fmt.Errorf("empty batch")
}

4
mcp/util.go
View file

@ -6,6 +6,8 @@ package mcp
import (
"encoding/json"
internaljson "github.com/modelcontextprotocol/go-sdk/internal/json"
)
func assert(cond bool, msg string) {
@ -21,7 +23,7 @@ func remarshal(from, to any) error {
if err != nil {
return err
}
if err := json.Unmarshal(data, to); err != nil {
if err := internaljson.Unmarshal(data, to); err != nil {
return err
}
return nil