vulnerability / NVI-00011837 / Revision 3
MCP TypeScript SDK: OAuth client could send credentials to an authorization server chosen by the MCP server
GitHub lists this reviewed advisory for @modelcontextprotocol/sdk, @modelcontextprotocol/client. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
7.5 high
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
7.5 HIGH (3.1)
security-advisories@github.com severity; no combined Null risk score.
0.226%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.13291. Missing scores are unknown.
As of · FIRST EPSS
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
@modelcontextprotocol/sdk
source listed>= 1.12.0, < 1.31.0
### 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 `OAuthT
@modelcontextprotocol/client
source listed>= 2.0.0, < 2.2.0
### 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 `OAuthT
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. FIRST EPSS
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
- NVD lastModified does not establish freshness of every associated CPE record.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-6qxp-vccf-f47h ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- CVE-2026-104850 ↗
NIST National Vulnerability Database · official catalog
Observed . This product uses data from the NVD API but is not endorsed or certified by the NVD.
- CVE-2026-104850 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 3 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 2 ·
Source facts changed; compare the preserved prior revision.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.