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.
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 2.2.0Upgrade to:
@modelcontextprotocol/sdk 1.32.0 or later@modelcontextprotocol/client 2.3.0 or laterRedirects 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' }).
| Software | Affected versions |
|---|---|
@modelcontextprotocol / sdk
|
< 1.32.0 |
@modelcontextprotocol / client
|
>= 2.0.0, < 2.3.0 |
A vulnerability database tells you what is broken. Attack surface management tells you where it is running: it discovers your internet-facing assets and flags the ones affected by issues like this one.
What is attack surface management? →A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.
CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.
A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.
Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.
Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.
SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.