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The Model Context Protocol (MCP) TypeScript SDK does not enable DNS rebinding protection by default for HTTP-based servers. When an HTTP-based MCP server is run on localhost without authentication with StreamableHTTPServerTransport or SSEServerTransport and has not enabled enableDnsRebindingProtection, a malicious website could exploit DNS rebinding to bypass same-origin policy restrictions and send requests to the local MCP server. This could allow an attacker to invoke tools or access resources exposed by the MCP server on behalf of the user in those limited circumstances.
Note that running HTTP-based MCP servers locally without authentication is not recommended per MCP security best practices. This issue does not affect servers using stdio transport.
Servers created via createMcpExpressApp() now have this protection enabled by default when binding to localhost. Users with custom Express configurations are advised to update to version 1.24.0 and apply the exported hostHeaderValidation() middleware when running an unauthenticated server on localhost.
A ReDoS vulnerability in the UriTemplate class allows attackers to cause denial of service. The partToRegExp() function generates a regex pattern with nested quantifiers (([^/]+(?:,[^/]+)*)) for exploded template variables (e.g., {/id*}, {?tags*}), causing catastrophic backtracking on malicious input.
Who is affected: MCP servers that register resource templates with exploded array patterns and accept requests from untrusted clients.
Attack result: An attacker sends a crafted URI via resources/read request, causing 100% CPU utilization, server hang/crash, and denial of service for all clients.
Affected Versions
All versions of @modelcontextprotocol/sdk prior to the patched release.
Patches
v1.25.2 contains b392f02ffcf37c088dbd114fedf25026ec3913d3 the fix modifies the regex pattern to prevent backtracking.
Workarounds
Avoid using exploded patterns ({/id*}, {?tags*}) in resource templates
Implement request timeouts and rate limiting
Validate URIs before processing to reject suspicious patterns
fix: normalize null to undefined in ElicitResultSchema content field by @mattzcarey in #1204
Modify Origin header validation in validateRequestHeaders (streamableHttp.ts and sse.ts) to allow requests without an Origin, as they are not relevant to server DNS rebinding protection. by @jacopoc in #1205
Disabled SSE priming events to fix backwards compatibility - 1.23.x clients crash on empty SSE data (JSON.parse(""))
This is a patch for servers still on 1.23.x that were breaking clients not handling the the 2025-11-25 priming event behavior with empty SSE data fields. See #1233 for more details.
fix: Prefer the token_endpoint_auth_method response from DCR registration by @chipgpt in #1022
Fix: Non-existent tool, disabled tool and inputSchema validation return MCP protocol level instead of CallToolResult with isError: true by @KKonstantinov in #1044
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This PR contains the following updates:
^0.5.0→^1.25.2GitHub Vulnerability Alerts
CVE-2025-66414
The Model Context Protocol (MCP) TypeScript SDK does not enable DNS rebinding protection by default for HTTP-based servers. When an HTTP-based MCP server is run on localhost without authentication with
StreamableHTTPServerTransportorSSEServerTransportand has not enabledenableDnsRebindingProtection, a malicious website could exploit DNS rebinding to bypass same-origin policy restrictions and send requests to the local MCP server. This could allow an attacker to invoke tools or access resources exposed by the MCP server on behalf of the user in those limited circumstances.Note that running HTTP-based MCP servers locally without authentication is not recommended per MCP security best practices. This issue does not affect servers using stdio transport.
Servers created via
createMcpExpressApp()now have this protection enabled by default when binding to localhost. Users with custom Express configurations are advised to update to version1.24.0and apply the exportedhostHeaderValidation()middleware when running an unauthenticated server on localhost.CVE-2026-0621
Impact
A ReDoS vulnerability in the
UriTemplateclass allows attackers to cause denial of service. ThepartToRegExp()function generates a regex pattern with nested quantifiers (([^/]+(?:,[^/]+)*)) for exploded template variables (e.g.,{/id*},{?tags*}), causing catastrophic backtracking on malicious input.Who is affected: MCP servers that register resource templates with exploded array patterns and accept requests from untrusted clients.
Attack result: An attacker sends a crafted URI via
resources/readrequest, causing 100% CPU utilization, server hang/crash, and denial of service for all clients.Affected Versions
All versions of
@modelcontextprotocol/sdkprior to the patched release.Patches
v1.25.2 contains b392f02ffcf37c088dbd114fedf25026ec3913d3 the fix modifies the regex pattern to prevent backtracking.
Workarounds
{/id*},{?tags*}) in resource templatesRelease Notes
modelcontextprotocol/typescript-sdk (@modelcontextprotocol/sdk)
v1.25.2Compare Source
What's Changed
New Contributors
Full Changelog: modelcontextprotocol/typescript-sdk@1.25.1...v1.25.2
v1.25.1Compare Source
What's Changed
Full Changelog: modelcontextprotocol/typescript-sdk@1.25.0...1.25.1
v1.25.0Compare Source
What's Changed
/testby @KKonstantinov in #1220New Contributors
Full Changelog: modelcontextprotocol/typescript-sdk@1.24.3...1.25.0
v1.24.3Compare Source
What's Changed
Full Changelog: modelcontextprotocol/typescript-sdk@1.24.2...1.24.3
v1.24.2Compare Source
What's Changed
New Contributors
Full Changelog: modelcontextprotocol/typescript-sdk@1.24.1...1.24.2
v1.24.1Compare Source
What's Changed
New Contributors
Full Changelog: modelcontextprotocol/typescript-sdk@1.24.0...1.24.1
v1.24.0Compare Source
Summary
This release brings us up to speed with the latest MCP spec
2025-11-25. Take a look at the latest spec as well as the release blog post.What's Changed
New Contributors
Full Changelog: modelcontextprotocol/typescript-sdk@1.23.0...1.24.0
v1.23.1Compare Source
Fixed:
This is a patch for servers still on 1.23.x that were breaking clients not handling the the
2025-11-25priming event behavior with empty SSEdatafields. See #1233 for more details.Full Changelog: modelcontextprotocol/typescript-sdk@1.23.0...1.23.1
v1.23.0Compare Source
What's Changed
.catchall()on inputSchema/outputSchema to support JSON Schema 2020-12 by @felixweinberger in #1135New Contributors
Full Changelog: modelcontextprotocol/typescript-sdk@1.22.0...1.23.0
v1.22.0Compare Source
What's Changed
registerTool: accept ZodType for input and output schema by @ksinder in #816New Contributors
Full Changelog: modelcontextprotocol/typescript-sdk@1.21.1...1.22.0
v1.21.2Compare Source
What's changed
This is a patch release for a regression highlighted by #1103
This patch contains only the cherry picked fix in #1108
Full Changelog: modelcontextprotocol/typescript-sdk@1.21.1...1.21.2
v1.21.1Compare Source
What's Changed
WWW-Authenticatescopeparam for SEP-835 by @chipgpt in #983New Contributors
Full Changelog: modelcontextprotocol/typescript-sdk@1.21.0...1.21.1
v1.21.0Compare Source
What's Changed
token_endpoint_auth_methodresponse from DCR registration by @chipgpt in #1022New Contributors
Full Changelog: modelcontextprotocol/typescript-sdk@1.20.2...1.21.0
v1.20.2Compare Source
What's Changed
New Contributors
Full Changelog: modelcontextprotocol/typescript-sdk@1.20.1...1.20.2
v1.20.1Compare Source
What's Changed
New Contributors
Full Changelog: modelcontextprotocol/typescript-sdk@1.20.0...1.20.1
v1.20.0Compare Source
What's Changed
New Contributors 🙏
Full Changelog: modelcontextprotocol/typescript-sdk@1.19.0...1.20.0
v1.19.1Compare Source
v1.18.2Compare Source
What's Changed
demoInMemoryOAuthProviderby @TylerLeonhardt in #931New Contributors
Full Changelog: modelcontextprotocol/typescript-sdk@1.18.1...1.18.2
v1.18.1Compare Source
What's Changed
New Contributors
Full Changelog: modelcontextprotocol/typescript-sdk@1.18.0...1.18.1
v1.18.0Compare Source
What's Changed
New Contributors
Full Changelog: modelcontextprotocol/typescript-sdk@1.17.5...1.18.0
v1.17.5Compare Source
What's Changed
Full Changelog: modelcontextprotocol/typescript-sdk@1.17.4...1.17.5
v1.17.4Compare Source
What's Changed
Full Changelog: modelcontextprotocol/typescript-sdk@1.17.3...1.17.4
v1.17.3Compare Source
What's Changed
New Contributors
Full Changelog: modelcontextprotocol/typescript-sdk@1.17.2...1.17.3
v1.17.2Compare Source
What's Changed
Full Changelog: modelcontextprotocol/typescript-sdk@1.17.1...1.17.2
v1.17.1Compare Source
What's Changed
Full Changelog: modelcontextprotocol/typescript-sdk@1.17.0...1.17.1
v1.17.0Compare Source
What's Changed
New Contributors 🙏
Full Changelog: modelcontextprotocol/typescript-sdk@1.16.0...1.17.0
v1.16.0Compare Source
What's Changed
invalidateCredentials()toOAuthClientProviderby @geelen in #570New Contributors 🙏
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