Vulnerability-Lookup

CVE-2026-104850 (GCVE-0-2026-104850)

Vulnerability from cvelistv5 – Published: 2026-10-06 16:08 – Updated: 2026-10-06 16:28

Title

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

Summary

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.

Severity

7.5 (High)


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

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-10-06 16:28 UTC

CWE

CWE-345 - Insufficient Verification of Data Authenticity
CWE-522 - Insufficiently Protected Credentials

Assigner

GitHub_M mitre root Scorecard

References

4 references

URL	Tags
https://github.com/modelcontextprotocol/typescrip…	x_refsource_CONFIRM
https://github.com/modelcontextprotocol/typescrip…	x_refsource_MISC
https://github.com/modelcontextprotocol/typescrip…	x_refsource_MISC
https://github.com/modelcontextprotocol/typescrip…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
modelcontextprotocol	typescript-sdk	Affected: >= 1.12.0, < 1.31.0 Affected: >= 2.0.0, < 2.2.0	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-104850

Vulnerability from fkie_nvd - Published: 2026-10-06 17:17 - Updated: 2026-10-06 20:03

Severity

7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/modelcontextprotocol/typescript-sdk/commit/edd12e282620ebf770d67316f19cf91d4112a1bd
	security-advisories@github.com	https://github.com/modelcontextprotocol/typescript-sdk/pull/2887
	security-advisories@github.com	https://github.com/modelcontextprotocol/typescript-sdk/releases/tag/v2.2.0
	security-advisories@github.com	https://github.com/modelcontextprotocol/typescript-sdk/security/advisories/GHSA-6qxp-vccf-f47h

Impacted products

	Vendor	Product	Version

JSON

To clipboard

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          "product": "typescript-sdk",
          "vendor": "modelcontextprotocol",
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  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Awaiting Analysis",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-345"
        },
        {
          "lang": "en",
          "value": "CWE-522"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}

GHSA-6QXP-VCCF-F47H

Vulnerability from github – Published: 2026-10-06 15:35 – Updated: 2026-10-06 15:35

Summary

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

Details

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.

Severity

7.5 (High)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "@modelcontextprotocol/sdk"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.12.0"
            },
            {
              "fixed": "1.31.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "@modelcontextprotocol/client"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.0.0"
            },
            {
              "fixed": "2.2.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-104850"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-345",
      "CWE-522"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-10-06T15:35:44Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Summary\nIn affected versions, the SDK\u0027s OAuth client let the MCP server decide which authorization server received the client\u0027s OAuth credentials. Credentials were not tied to the authorization server they belong to.\n\nA malicious or compromised MCP server could name its own authorization server. With no user interaction, the client would send it:\n\n- the `refresh_token` and `client_secret` stored from an earlier sign-in\n- the `client_secret` or signed assertion configured on a bundled provider\n\n### Am I affected?\nYes, if both of these hold:\n\n- your application uses the SDK\u0027s OAuth client over HTTP, through any of:\n    - an `authProvider` on a transport\n    - the `withOAuth()` middleware\n    - direct calls to `auth()` or `fetchToken()`\n- it may connect to an MCP server you do not fully trust while holding credentials for a legitimate authorization server\n\nAffected versions:\n\n- `@modelcontextprotocol/sdk` 1.12.0 through 1.30.1\n- `@modelcontextprotocol/client` 2.0.0 through 2.1.0, only for:\n    - bundled providers without `expectedIssuer`\n    - credentials stored or supplied without `issuer`\n    - direct calls to `fetchToken()`\n    - providers that read storage back through `OAuthTokensSchema` or `OAuthClientInformationSchema`\n\nNot affected:\n\n- MCP servers built with the SDK\n- stdio clients\n\n### Fix\nUpgrade to:\n\n- 1.x: `@modelcontextprotocol/sdk` 1.31.0 or later\n- 2.x: `@modelcontextprotocol/client` 2.2.0 or later, and `@modelcontextprotocol/core` 2.2.0 or later if you import it directly\n\nThe 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.\n\nIn the following cases, upgrading to the patched version is not enough. You also need to make a change:\n\n- **Bundled providers** (`ClientCredentialsProvider`, `PrivateKeyJwtProvider`, `StaticPrivateKeyJwtProvider`, `CrossAppAccessProvider`): pass `expectedIssuer`, for example `expectedIssuer: \u0027https://auth.example.com\u0027`. Without it they still use whichever authorization server the MCP server names.\n- **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.\n- **Your own `OAuthClientProvider`:** save exactly what `saveTokens()` and `saveClientInformation()` are given, including `issuer`. For pre-registered credentials, include `issuer` in what `clientInformation()` returns.\n\nNot covered by this fix:\n\n- a new interactive sign-in, which still goes to the authorization server the MCP server names. Only complete sign-ins for servers you trust.\n- `refreshAuthorization()` and `exchangeAuthorization()` called directly\n- 2.x with `skipIssuerMetadataValidation: true`\n\nIf an affected client may have connected to an untrusted MCP server, rotate its client secret or signing key and revoke its tokens.\n\nIf you cannot upgrade yet, connect OAuth clients only to MCP servers you trust. 2.0.0 and 2.1.0 already accept `expectedIssuer`.",
  "id": "GHSA-6qxp-vccf-f47h",
  "modified": "2026-10-06T15:35:44Z",
  "published": "2026-10-06T15:35:44Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/modelcontextprotocol/typescript-sdk/security/advisories/GHSA-6qxp-vccf-f47h"
    },
    {
      "type": "WEB",
      "url": "https://github.com/modelcontextprotocol/typescript-sdk/pull/2887"
    },
    {
      "type": "WEB",
      "url": "https://github.com/modelcontextprotocol/typescript-sdk/commit/edd12e282620ebf770d67316f19cf91d4112a1bd"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/modelcontextprotocol/typescript-sdk"
    },
    {
      "type": "WEB",
      "url": "https://github.com/modelcontextprotocol/typescript-sdk/releases/tag/v2.2.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "MCP TypeScript SDK: OAuth client could send credentials to an authorization server chosen by the MCP server"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

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Action not permitted

CVE-2026-104850 (GCVE-0-2026-104850)

FKIE_CVE-2026-104850

GHSA-6QXP-VCCF-F47H

Summary

Am I affected?

Fix

Tags

Sightings

Nomenclature

Related by attack behaviour