MCP TypeScript client SDK: HTTP client transports and OAuth requests followed cross-origin redirects and re-sent custom headers and request bodies
CVSS score
6.5
EPSS probability
—
Risk score
0.7
Published
3 h ago
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Vulnerability description
DayBreach AI Explanation
Verified against sourcesSources read
1
Source agreement
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Evidence confidence
%55
Short explanation
A vulnerability in the MCP TypeScript client SDK causes HTTP client transports and OAuth requests to follow cross-origin redirects and re-send custom headers and request bodies.
This vulnerability can lead to the exposure of sensitive information such as authentication secrets and API keys to external servers.
What should be done?
- Upgrade @modelcontextprotocol/sdk to version 1.32.0 or later
- Upgrade @modelcontextprotocol/client to version 2.3.0 or later
- Pass a fetch function that refuses redirects as a temporary workaround
Chain of evidence and sources
Etkilenen sürümlerde HTTP istemci aktarımları ve OAuth istekleri herhangi bir orijine yönlendirmeleri takip etmektedir.
307 veya 308 yönlendirmelerinde refresh_token ve client_secret gibi istek gövdeleri de harici hedeflere ulaşabilmektedir.
stdio istemcileri bu zafiyetten etkilenmemektedir.
Show the technical text from the sources
### Summary In affected versions, the SDK's HTTP client transports and OAuth requests followed redirects to any origin. If an MCP server or authorization server redirected a request to another origin, that origin received custom request headers (such as an `X-API-Key` set in `requestInit.headers`) and the `mcp-session-id` header. On a `307` or `308` it also received the request body, including OAuth token requests with their `refresh_token` and `client_secret`. On current runtimes `fetch` already drops the `Authorization` header across origins. ### Am I affected? Yes, if your application uses `StreamableHTTPClientTransport`, `SSEClientTransport`, or the SDK's OAuth client functions such as `auth()`. stdio clients are not affected. Affected versions: - `@modelcontextprotocol/sdk` all versions through 1.31.0 - `@modelcontextprotocol/client` 2.0.0 through 2.2.0 ### Fix Upgrade to: - 1.x: `@modelcontextprotocol/sdk` 1.32.0 or later - 2.x: `@modelcontextprotocol/client` 2.3.0 or later Redirects are now followed only within the same origin, and not at all in browsers. If your MCP server or authorization server redirects to another origin on purpose, configure the final URL instead. Setting `redirectPolicy: 'follow'` on a transport restores the old behaviour and the exposure. If a redirect may have reached a host you do not control, rotate the API keys and `client_secret` your application held and revoke its tokens. If you cannot upgrade yet, pass a `fetch` that refuses redirects, for example `(url, init) => fetch(url, { ...init, redirect: 'error' })`.
CVSS vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N
CWE: CWE-200
This explanation was compiled automatically from the source records. Scores, active exploitation, patch and exploit status come straight from the sources.
IMPACT: Affected Products and Software
RED HAT CSAF/VEX: Product Impact Check
SCORING: CVSS from Multiple Sources
CVSS Scores
The Common Vulnerability Scoring System is a standardised framework for assessing the severity of vulnerabilities in software and systems. We collect and display CVSS scores from several sources for each CVE.
| SCORE | VERSION | SEVERITY | VECTOR | SOURCE |
|---|---|---|---|---|
| 6.5 | CVSS 3.x | — | Vector not published | GitHub Advisory |
| 0.0 | CVSS 4.0 | — | Vector not published | GitHub Advisory |
Patch and Remediation Guide
Solution & Remediation Advisory
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Public exploit and active exploitation status
Verified exploit intelligence
No verified public PoC, exploit repository or Metasploit module has been found for this CVE yet.
Weakness Classification and Attack Patterns (CWE & CAPEC)
CWE - Common Weakness Enumeration
While CVE identifies specific instances of vulnerabilities, CWE categorises the common flaws or weaknesses that can lead to vulnerabilities. CVE-2026-111769 is associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification (CAPEC) stores attack patterns, which are descriptions of the common attributes and approaches employed by adversaries to exploit the CVE-2026-111769 weaknesses.
Attack Vector and Accessibility
Official Sources and Advisories
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