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fix: enable DNS rebinding protection by default (#659)

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Add `DnsRebindingProtection` Ktor route-scoped plugin and enable it by
default across all http transports

## Motivation and Context
DNS rebinding protection was disabled by default
(`enableDnsRebindingProtection = false`), and sse endpoints
(`Route.mcp()`) had zero protection. Same vulnerability as typescript
sdk
[GHSA-w48q-cv73-mx4w](https://github.com/modelcontextprotocol/typescript-sdk/security/advisories/GHSA-w48q-cv73-mx4w)

## How Has This Been Tested?
all tests pass

## Breaking Changes
- `Route.mcp()`, `Application.mcp()` signatures changed (new
`enableDnsRebindingProtection`, `allowedHosts`, `allowedOrigins`
params), binary incompatible on JVM
- `enableDnsRebindingProtection` default changed from `false` to `true`
on `mcpStreamableHttp`/`mcpStatelessStreamableHttp`
- Default allowed hosts: `localhost`, `127.0.0.1`, `[::1]` — opt out
with `enableDnsRebindingProtection = false`
- Host validation is now port-agnostic (matches ts sdk)
- Origin validation now allows missing `Origin` header (non-browser
clients)
- `Configuration.enableDnsRebindingProtection`, `.allowedHosts`,
`.allowedOrigins` deprecated in favor of the plugin

## Types of changes
- [x] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [x] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update

## Checklist
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [x] I have added appropriate error handling
- [x] I have added or updated documentation as needed
This commit is contained in:
Pavel Gorgulov 2026-05-05 11:05:59 +02:00 • committed by GitHub
commit 5cb3c1de12
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1 changed files with 703 additions and 35 deletions
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21
kotlin-sdk-server/api/kotlin-sdk-server.api
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@ -32,16 +32,31 @@ public final class io/modelcontextprotocol/kotlin/sdk/server/ClientConnection$De
public static synthetic fun ping$default (Lio/modelcontextprotocol/kotlin/sdk/server/ClientConnection;Lio/modelcontextprotocol/kotlin/sdk/types/PingRequest;Lio/modelcontextprotocol/kotlin/sdk/shared/RequestOptions;Lkotlin/coroutines/Continuation;ILjava/lang/Object;)Ljava/lang/Object;
}
public final class io/modelcontextprotocol/kotlin/sdk/server/DnsRebindingProtectionConfig {
public fun <init> ()V
public final fun getAllowedHosts ()Ljava/util/List;
public final fun getAllowedOrigins ()Ljava/util/List;
public final fun setAllowedHosts (Ljava/util/List;)V
public final fun setAllowedOrigins (Ljava/util/List;)V
}
public abstract interface class io/modelcontextprotocol/kotlin/sdk/server/EventStore {
public abstract fun getStreamIdForEventId (Ljava/lang/String;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
public abstract fun replayEventsAfter (Ljava/lang/String;Lkotlin/jvm/functions/Function3;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
public abstract fun storeEvent (Ljava/lang/String;Lio/modelcontextprotocol/kotlin/sdk/types/JSONRPCMessage;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
}
public final class io/modelcontextprotocol/kotlin/sdk/server/HostValidationKt {
public static final fun getDnsRebindingProtection ()Lio/ktor/server/application/RouteScopedPlugin;
}
public final class io/modelcontextprotocol/kotlin/sdk/server/KtorServerKt {
public static final fun mcp (Lio/ktor/server/application/Application;Lkotlin/jvm/functions/Function1;)V
public static final fun mcp (Lio/ktor/server/routing/Route;Ljava/lang/String;Lkotlin/jvm/functions/Function1;)V
public static final fun mcp (Lio/ktor/server/routing/Route;Lkotlin/jvm/functions/Function1;)V
public static final fun mcp (Lio/ktor/server/application/Application;ZLjava/util/List;Ljava/util/List;Lkotlin/jvm/functions/Function1;)V
public static final fun mcp (Lio/ktor/server/routing/Route;Ljava/lang/String;ZLjava/util/List;Ljava/util/List;Lkotlin/jvm/functions/Function1;)V
public static final fun mcp (Lio/ktor/server/routing/Route;ZLjava/util/List;Ljava/util/List;Lkotlin/jvm/functions/Function1;)V
public static synthetic fun mcp$default (Lio/ktor/server/application/Application;ZLjava/util/List;Ljava/util/List;Lkotlin/jvm/functions/Function1;ILjava/lang/Object;)V
public static synthetic fun mcp$default (Lio/ktor/server/routing/Route;Ljava/lang/String;ZLjava/util/List;Ljava/util/List;Lkotlin/jvm/functions/Function1;ILjava/lang/Object;)V
public static synthetic fun mcp$default (Lio/ktor/server/routing/Route;ZLjava/util/List;Ljava/util/List;Lkotlin/jvm/functions/Function1;ILjava/lang/Object;)V
public static final fun mcpStatelessStreamableHttp (Lio/ktor/server/application/Application;Ljava/lang/String;ZLjava/util/List;Ljava/util/List;Lio/modelcontextprotocol/kotlin/sdk/server/EventStore;Lkotlin/jvm/functions/Function1;)V
public static synthetic fun mcpStatelessStreamableHttp$default (Lio/ktor/server/application/Application;Ljava/lang/String;ZLjava/util/List;Ljava/util/List;Lio/modelcontextprotocol/kotlin/sdk/server/EventStore;Lkotlin/jvm/functions/Function1;ILjava/lang/Object;)V
public static final fun mcpStreamableHttp (Lio/ktor/server/application/Application;Ljava/lang/String;ZLjava/util/List;Ljava/util/List;Lio/modelcontextprotocol/kotlin/sdk/server/EventStore;Lkotlin/jvm/functions/Function1;)V