MCP TypeScript SDK: OAuth client could send credentials to an authorization server chosen by the MCP server

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

MCP TypeScript SDK is the official TypeScript SDK for Model Context Protocol servers and clients. Starting in version 1.12.0 and prior to versions 1.31.0 and 2.2.0, the SDK's OAuth client support let the MCP server a client connected to decide which authorization server received the client's OAuth credentials. Stored and pre-provisioned credentials were not bound to the authorization server they belong to. A malicious or compromised MCP server could name its own authorization server in its protected resource metadata. Without any user interaction, the client would send that server the `refresh_token` and `client_secret` stored from an earlier sign-in (1.x), or the configured `client_secret` or signed assertion of a bundled non-interactive provider (1.x and 2.x). Only those applications that use the SDK as an MCP client over HTTP with an `authProvider`: your own `OAuthClientProvider`, or the bundled `ClientCredentialsProvider`, `PrivateKeyJwtProvider`, `StaticPrivateKeyJwtProvider` or (2.x) `CrossAppAccessProvider` and that may connect to an MCP server the owners does not fully trust while holding credentials for a legitimate authorization server are affected. `@modelcontextprotocol/sdk` 1.31.0 (1.x) and `@modelcontextprotocol/client` 2.2.0 (2.x) patch the issue. A workaround for those who cannot upgrade is available. 2.0.0 and 2.1.0 already accept `expectedIssuer`. On 1.x, the only workaround is to connect OAuth-enabled clients only to MCP servers you trust.

Source published

6 Oct 2026 16:08:21 UTC

Source modified

6 Oct 2026 16:28:53 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

MCP TypeScript SDK is the official TypeScript SDK for Model Context Protocol servers and clients. Starting in version 1.12.0 and prior to versions 1.31.0 and 2.2.0, the SDK's OAuth client support let the MCP server a client connected to decide which authorization server received the client's OAuth credentials. Stored and pre-provisioned credentials were not bound to the authorization server they belong to. A malicious or compromised MCP server could name its own authorization server in its protected resource metadata. Without any user interaction, the client would send that server the `refresh_token` and `client_secret` stored from an earlier sign-in (1.x), or the configured `client_secret` or signed assertion of a bundled non-interactive provider (1.x and 2.x). Only those applications that use the SDK as an MCP client over HTTP with an `authProvider`: your own `OAuthClientProvider`, or the bundled `ClientCredentialsProvider`, `PrivateKeyJwtProvider`, `StaticPrivateKeyJwtProvider` or (2.x) `CrossAppAccessProvider` and that may connect to an MCP server the owners does not fully trust while holding credentials for a legitimate authorization server are affected. `@modelcontextprotocol/sdk` 1.31.0 (1.x) and `@modelcontextprotocol/client` 2.2.0 (2.x) patch the issue. A workaround for those who cannot upgrade is available. 2.0.0 and 2.1.0 already accept `expectedIssuer`. On 1.x, the only workaround is to connect OAuth-enabled clients only to MCP servers you trust.

Source published

Oct 6, 2026, 4:08:21 PM (timezone not stated)

Source modified

Oct 6, 2026, 4:28:53 PM (timezone not stated)

Observed here

11 Nov 2026 05:30:29 UTC

Source terms

ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 3.1 · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

MCP TypeScript SDK is the official TypeScript SDK for Model Context Protocol servers and clients. Starting in version 1.12.0 and prior to versions 1.31.0 and 2.2.0, the SDK's OAuth client support let the MCP server a client connected to decide which authorization server received the client's OAuth credentials. Stored and pre-provisioned credentials were not bound to the authorization server they belong to. A malicious or compromised MCP server could name its own authorization server in its protected resource metadata. Without any user interaction, the client would send that server the `refresh_token` and `client_secret` stored from an earlier sign-in (1.x), or the configured `client_secret` or signed assertion of a bundled non-interactive provider (1.x and 2.x). Only those applications that use the SDK as an MCP client over HTTP with an `authProvider`: your own `OAuthClientProvider`, or the bundled `ClientCredentialsProvider`, `PrivateKeyJwtProvider`, `StaticPrivateKeyJwtProvider` or (2.x) `CrossAppAccessProvider` and that may connect to an MCP server the owners does not fully trust while holding credentials for a legitimate authorization server are affected. `@modelcontextprotocol/sdk` 1.31.0 (1.x) and `@modelcontextprotocol/client` 2.2.0 (2.x) patch the issue. A workaround for those who cannot upgrade is available. 2.0.0 and 2.1.0 already accept `expectedIssuer`. On 1.x, the only workaround is to connect OAuth-enabled clients only to MCP servers you trust.

Source published

6 Oct 2026 17:17:15 UTC

Source modified

6 Oct 2026 20:03:40 UTC

Observed here

25 Oct 2026 04:17:29 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

### Summary In affected versions, the SDK's OAuth client let the MCP server decide which authorization server received the client's OAuth credentials. Credentials were not tied to the authorization server they belong to. A malicious or compromised MCP server could name its own authorization server. With no user interaction, the client would send it: - the `refresh_token` and `client_secret` stored from an earlier sign-in - the `client_secret` or signed assertion configured on a bundled provider ### Am I affected? Yes, if both of these hold: - your application uses the SDK's OAuth client over HTTP, through any of: - an `authProvider` on a transport - the `withOAuth()` middleware - direct calls to `auth()` or `fetchToken()` - it may connect to an MCP server you do not fully trust while holding credentials for a legitimate authorization server Affected versions: - `@modelcontextprotocol/sdk` 1.12.0 through 1.30.1 - `@modelcontextprotocol/client` 2.0.0 through 2.1.0, only for: - bundled providers without `expectedIssuer` - credentials stored or supplied without `issuer` - direct calls to `fetchToken()` - providers that read storage back through `OAuthTokensSchema` or `OAuthClientInformationSchema` Not affected: - MCP servers built with the SDK - stdio clients ### Fix Upgrade to: - 1.x: `@modelcontextprotocol/sdk` 1.31.0 or later - 2.x: `@modelcontextprotocol/client` 2.2.0 or later, and `@modelcontextprotocol/core` 2.2.0 or later if you import it directly The client now records the authorization server as `issuer` on saved credentials and does not send them to a different one. The user signs in again, or the call throws. In the following cases, upgrading to the patched version is not enough. You also need to make a change: - **Bundled providers** (`ClientCredentialsProvider`, `PrivateKeyJwtProvider`, `StaticPrivateKeyJwtProvider`, `CrossAppAccessProvider`): pass `expectedIssuer`, for example `expectedIssuer: 'https://auth.example.com'`. Without it they still use whichever authorization server the MCP server names. - **Credentials saved without `issuer`:** tokens and client information your `OAuthClientProvider` persisted (file, keychain, database) before upgrading, including everything 1.x saved before 1.31.0. They still go to whichever authorization server is named at first use. Add `issuer` to them, or clear them so users sign in again. - **Your own `OAuthClientProvider`:** save exactly what `saveTokens()` and `saveClientInformation()` are given, including `issuer`. For pre-registered credentials, include `issuer` in what `clientInformation()` returns. Not covered by this fix: - a new interactive sign-in, which still goes to the authorization server the MCP server names. Only complete sign-ins for servers you trust. - `refreshAuthorization()` and `exchangeAuthorization()` called directly - 2.x with `skipIssuerMetadataValidation: true` If an affected client may have connected to an untrusted MCP server, rotate its client secret or signing key and revoke its tokens. If you cannot upgrade yet, connect OAuth clients only to MCP servers you trust. 2.0.0 and 2.1.0 already accept `expectedIssuer`.

Source published

6 Oct 2026 15:35:44 UTC

Source modified

6 Oct 2026 15:46:47 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Publisher rating · HIGH