Summary
MCP TypeScript client SDK: HTTP client transports and OAuth requests followed cross-origin redirects and re-sent custom headers and request bodies
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/sdkall versions through 1.31.0@modelcontextprotocol/client2.0.0 through 2.2.0
Impact
CVE-2026-111769 has a CVSS score of 6.5 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.32.0, 2.3.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
Upgrade to:
- 1.x:
@modelcontextprotocol/sdk1.32.0 or later - 2.x:
@modelcontextprotocol/client2.3.0 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' }).
Frequently Asked Questions
- What is CVE-2026-111769? CVE-2026-111769 is a medium-severity security vulnerability in @modelcontextprotocol/sdk (npm), affecting versions < 1.32.0. It is fixed in 1.32.0, 2.3.0.
- How severe is CVE-2026-111769? CVE-2026-111769 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which packages are affected by CVE-2026-111769?
@modelcontextprotocol/sdk(npm) (versions < 1.32.0)@modelcontextprotocol/client(npm) (versions >= 2.0.0, < 2.3.0)
- Is there a fix for CVE-2026-111769? Yes. CVE-2026-111769 is fixed in 1.32.0, 2.3.0. Upgrade to this version or later.
- Is CVE-2026-111769 exploitable, and should I be worried? Whether CVE-2026-111769 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-111769 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-111769?
- Upgrade
@modelcontextprotocol/sdkto 1.32.0 or later - Upgrade
@modelcontextprotocol/clientto 2.3.0 or later
- Upgrade