fix(deps): update dependency fastmcp to v3 [security] - #864
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Run report for bf7ad75d
|
| Action | Time | Status | Info | |
|---|---|---|---|---|
| 🟩 | SyncWorkspace |
15.8ms | Passed | |
| 🟩 | SyncProject(vendir) |
0.6ms | Passed | |
| 🟩 | SyncProject(devenv) |
0.4ms | Passed | |
| 🟦 | RunTask(vendir:build) |
21.1s | Cached | |
| 🟩 | RunTask(devenv:apply) |
4m 40s | Passed | SLOW |
| 🟦 | RunTask(devenv:test) |
257.2ms | Cached |
Environment
OS: macOS
Matrix:
os = macos-latest
name = macOS
index = 0
total = 1
job_number = 1
Variables:
MOON_TOOLCHAIN_FORCE_GLOBALS = true
Touched files
libs/fleet-mcp/pyproject.toml
Run report for bf7ad75d
|
| Action | Time | Status | Info | |
|---|---|---|---|---|
| 🟩 | SyncWorkspace |
8.6ms | Passed | |
| 🟩 | SyncProject(devcontainer) |
0.5ms | Passed | |
| 🟩 | SyncProject(fleet-mcp) |
0.7ms | Passed | |
| 🟦 | RunTask(talos-image:generate-sha) |
860.7ms | Cached | |
| 🟦 | RunTask(devcontainers-cli:build) |
1.8s | Cached | |
| 🟩 | RunTask(docker:buildx_run) |
1.9s | Passed | |
| 🟦 | RunTask(fleet-mcp:build) |
1.2s | Cached | |
| 🟥 | RunTask(fleet-mcp:lint) |
8.8s | Failed | |
| 🟦 | RunTask(vendir:build) |
24s | Cached | |
| 🟦 | RunTask(vendir:test) |
171.2ms | Cached | |
| 🟦 | RunTask(talos-image:generate-profile) |
251.1ms | Cached | |
| 🟦 | RunTask(devcontainer:build) |
687.9ms | Cached | |
| 🟦 | RunTask(devcontainer:test) |
209.2ms | Cached | |
| 🟩 | RunTask(devenv:apply) |
22.3s | Passed |
Environment
OS: Linux
Matrix:
os = ubuntu-latest
name = Linux
index = 0
total = 2
job_number = 1
Variables:
MOON_TOOLCHAIN_FORCE_GLOBALS = true
Touched files
libs/fleet-mcp/pyproject.toml
Run report for bf7ad75d
|
| Action | Time | Status | Info | |
|---|---|---|---|---|
| 🟩 | SyncWorkspace |
8.9ms | Passed | |
| 🟩 | SyncProject(fleet-mcp) |
0.5ms | Passed | |
| 🟩 | SyncProject(devcontainer) |
0.9ms | Passed | |
| 🟩 | SyncProject(escaperoom) |
0.3ms | Passed | |
| 🟦 | RunTask(talos-image:generate-sha) |
1.5s | Cached | |
| 🟩 | RunTask(docker:buildx_run) |
1.8s | Passed | |
| 🟦 | RunTask(escaperoom:test) |
275.1ms | Cached | |
| 🟦 | RunTask(devcontainers-cli:build) |
3s | Cached | |
| 🟥 | RunTask(fleet-mcp:test) |
8s | Failed | |
| 🟦 | RunTask(vendir:build) |
32.3s | Cached | |
| 🟦 | RunTask(vendir:test) |
204.9ms | Cached | |
| 🟦 | RunTask(talos-image:generate-profile) |
280.6ms | Cached | |
| 🟦 | RunTask(devcontainer:build) |
485.5ms | Cached | |
| 🟩 | RunTask(devenv:apply) |
20.8s | Passed |
Environment
OS: Linux
Matrix:
os = ubuntu-latest
name = Linux
index = 1
total = 2
job_number = 2
Variables:
MOON_TOOLCHAIN_FORCE_GLOBALS = true
Touched files
libs/fleet-mcp/pyproject.toml
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This PR contains the following updates:
==2.13.0.2→==3.2.0Warning
Some dependencies could not be looked up. Check the Dependency Dashboard for more information.
FastMCP updated to MCP 1.23+ due to CVE-2025-66416
GHSA-rcfx-77hg-w2wv
More information
Details
There was a recent CVE report on MCP: https://nvd.nist.gov/vuln/detail/CVE-2025-66416.
FastMCP does not use any of the affected components of the MCP SDK directly. However, FastMCP versions prior to 2.14.0 did allow MCP SDK versions <1.23 that were vulnerable to CVE-2025-66416. Users should upgrade to FastMCP 2.14.0 or later.
Severity
High
References
This data is provided by the GitHub Advisory Database (CC-BY 4.0).
FastMCP OAuth Proxy token reuse across MCP servers
CVE-2025-69196 / GHSA-5h2m-4q8j-pqpj
More information
Details
While testing the OAuth Proxy implementation, it was noticed that the server does not properly respect the
resourceparameter submitted by the client in the authorization and token request. Instead of issuing the token explicitly for this MCP server, the token is issued for thebase_urlpassed to theOAuthProxyduring initialization.Affected File:
https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/auth/oauth_proxy.py#L828
Affected Code:
Since the issued access and refresh tokens do not include information about the resource the token was issued for, it is impossible for the MCP server to properly verify whether the token was issued for it, hence violating the requirement of doing so demanded by the specification. Being able to verify whether the token was issued for the target MCP server enforces the protections offered by the steps proposed by the specification and the Resource Indicators OAuth extension.
Therefore, this misconfiguration exposes all MCP server setups using the FastMCP OAuth Proxy to an attack where an adversary creates a malicious MCP server that advertises the benign OAuth Proxy authorization server as its own authorization server. Once a victim completes an OAuth flow with this malicious MCP server, authenticating against the AS, the adversary can extract the token received at the malicious MCP server and use it to access other MCP servers (the benign ones) that also use the same AS, including the tools and resources they expose.
Steps to reproduce:
mcp-server-proxy.pyscript.python3 mcp-server-proxy.py.python3 mal_auth_server.py.python3 attacker_server.py.python3 client.py.Impact
This vulnerability allows an adversary to steal a victim’s authentication material for a benign MCP server using the FastMCP OAuth Proxy. The severity of this issue was decreased to Medium due to the consent screen showing the name of the MCP server the OAuth Proxy was intended for. However, a victim might not see it or get otherwise convinced by the attacker to ignore it, and overall this does not act as a proper mitigation for this issue.
Mitigation
To mitigate this vulnerability, it is recommended to issue tokens specifically for the MCP server submitted in the authorization URL’s
resourceGET parameter. In this way, the receiving MCP server will be able to properly verify that the token was indeed issued for it, allowing it to reject tokens stolen by an attack like the one demonstrated above.Severity
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:NReferences
This data is provided by the GitHub Advisory Database (CC-BY 4.0).
FastMCP has a Command Injection vulnerability - Gemini CLI
CVE-2025-64340 / GHSA-m8x7-r2rg-vh5g
More information
Details
Server names containing shell metacharacters (e.g.,
&) can cause command injection on Windows when passed tofastmcp install claude-codeorfastmcp install gemini-cli. These install paths usesubprocess.run()with a list argument, but on Windows the target CLIs often resolve to.cmdwrappers that are executed throughcmd.exe, which interprets metacharacters in the flattened command string.PoC:
On Windows, this opens Calculator via the
&calcin the server name.Impact:
Arbitrary command execution with the privileges of the user running
fastmcp install. Affects Windows hosts where the target CLI (one of claude, gemini) is installed as a.cmdwrapper. Does not affect macOS/Linux, and does not affect config-file-based install targets (cursor, goose, mcp-json).Patched in #3522 by validating server names to reject shell metacharacters.
Severity
CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:HReferences
This data is provided by the GitHub Advisory Database (CC-BY 4.0).
FastMCP: Missing Consent Verification in OAuth Proxy Callback Facilitates Confused Deputy Vulnerabilities
CVE-2026-27124 / GHSA-rww4-4w9c-7733
More information
Details
Summary
While testing the GitHubProvider OAuth integration, which allows authentication to a FastMCP MCP server via a FastMCP OAuthProxy using GitHub OAuth, it was discovered that the FastMCP OAuthProxy does not properly validate the user's consent upon receiving the authorization code from GitHub. In combination with GitHub’s behavior of skipping the consent page for previously authorized clients, this introduces a Confused Deputy vulnerability.
Technical Details
An adversary can initiate an authentication flow by connecting their malicious MCP client to a benign MCP server using the GitHubProvider OAuth integration. During this flow, the attacker consents to connect their client to the MCP server and, at that point, can capture the GitHub authorization URL they are redirected to after granting consent. The attacker can then lure a victim, who is already logged into GitHub and has previously connected an MCP client to the benign MCP server, to open this captured URL. As a result, the victim’s browser is immediately redirected to the OAuthProxy’s callback endpoint, which does not correctly enforce that this browser has just given consent. The OAuthProxy then redirects the victim’s browser to the malicious MCP client’s callback URL with a valid authorization code. The attacker can exchange this code for an access token to the benign MCP server associated with the victim’s GitHub account, potentially gaining unauthorized access to resources tied to that account.
Although this issue was verified in practice only for the GitHubProvider, a review of the source code, specifically the
OAuthProxy._handle_idp_callbackfunction, shows that the IdP callback handler does not verify whether the browser sending thestateandcodehas previously consented to connecting the client to the server. As long as a validstateandcodepair is provided, the OAuthProxy requests an access token from the IdP and then redirects the user-agent to the client’s callback URL with a newcodeand the correspondingstate, allowing the client to retrieve the access token from the proxy. This pattern causes all OAuth integrations whose IdP allows skipping the consent page to be vulnerable to this attack.Skipping the consent page is not, by itself, a vulnerability on the IdP side. Many providers legitimately skip consent for first-party or previously authorized clients with the same scopes. In this case, the core problem lies in the OAuthProxy callback handler not correctly verifying that the browser issuing the callback request is the same one that has just given the required consent.
Steps to reproduce
In a more realistic scenario, the malicious client could be a public MCP client or a simple web server that logs the received authorization code or token, which the attacker then uses to obtain the access token and connect to the MCP server as the victim.
Recommendation
To mitigate this issue, the OAuthProxy should verify that the browser sending the authorization code has actually given consent for the corresponding client. This can be achieved by setting and validating a consent cookie or similar browser-bound state, as described in the mitigations section for this vulnerability in the MCP specification.
Severity
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:NReferences
This data is provided by the GitHub Advisory Database (CC-BY 4.0).
FastMCP OpenAPI Provider has an SSRF & Path Traversal Vulnerability
CVE-2026-32871 / GHSA-vv7q-7jx5-f767
More information
Details
Technical Description
The
OpenAPIProviderin FastMCP exposes internal APIs to MCP clients by parsing OpenAPI specifications. TheRequestDirectorclass is responsible for constructing HTTP requests to the backend service.A critical vulnerability exists in the
_build_url()method. When an OpenAPI operation defines path parameters (e.g.,/api/v1/users/{user_id}), the system directly substitutes parameter values into the URL template string without URL-encoding. Subsequently,urllib.parse.urljoin()resolves the final URL.Since
urljoin()interprets../sequences as directory traversal, an attacker controlling a path parameter can perform path traversal attacks to escape the intended API prefix and access arbitrary backend endpoints. This results in authenticated SSRF, as requests are sent with the authorization headers configured in the MCP provider.Vulnerable Code
File:
fastmcp/utilities/openapi/director.pyRoot Cause
urllib.parse.urljoin()interprets../as directory traversalProof of Concept
Step 1: Backend API Setup
Create
internal_api.pyto simulate a vulnerable backend server:Step 2: Exploitation Script
Create
exploit_poc.py:Expected Output
The attacker successfully accessed an endpoint not defined in the OpenAPI specification using the MCP provider's authentication credentials.
Impact Assessment
Severity Justification
Attack Scenarios
Remediation
Recommended Fix
URL-encode all path parameter values before substitution to ensure reserved characters (
/,.,?,#) are treated as literal data, not path delimiters.Updated code for
_build_url()method:Severity
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:HReferences
This data is provided by the GitHub Advisory Database (CC-BY 4.0).
Release Notes
PrefectHQ/fastmcp (fastmcp)
v3.2.0: : Show Don't ToolCompare Source
FastMCP 3.2 is the Apps release. The 3.0 architecture gave you providers and transforms; 3.1 shipped Code Mode for tool discovery. 3.2 puts a face on it: your tools can now return interactive UIs — charts, dashboards, forms, maps — rendered right inside the conversation.
FastMCPApp
FastMCPAppis a new provider class for building interactive applications inside MCP. It separates the tools the LLM sees (@app.ui()) from the backend tools the UI calls (@app.tool()), manages visibility automatically, and gives tool references stable identifiers that survive namespace transforms and server composition — without requiring host cooperation.The UI is built with Prefab, a Python component library that compiles to interactive UIs. You write Python; the user sees charts, tables, forms, and dashboards. FastMCP handles the MCP Apps protocol machinery — renderer resources, CSP configuration, structured content serialization — so you don't have to.
For simpler cases where you just want to visualize data without server interaction, set
app=Trueon any tool and return Prefab components directly:Built-in Providers
Five ready-made providers you add with a single
add_provider()call:Dev Server
fastmcp dev appslaunches a browser-based preview for your app tools — pick a tool, provide arguments, and see the rendered UI without connecting to an MCP host. Includes an MCP message inspector for debugging the protocol traffic.Security
This release includes a significant security hardening pass: SSRF/path traversal prevention, JWT algorithm restrictions, OAuth scope enforcement, CSRF fixes, and more. See the changelog for the full list.
Everything Else
forward_resourceflag on all OAuth providers for IdPs that don't support RFC 8707. Clerk auth provider.FileResourceencoding parameter. SSLverifyparameter.client_log_levelsetting. MCP conformance tests in CI. And contributions from 13 new contributors.What's Changed
New Features 🎉
Breaking Changes⚠️
Enhancements ✨
--config-pathflag to claude-desktop install command by @Sumanshu-Nankana in #3380verifyparameter for SSL certificate configuration by @jlowin in #3487Security 🔒
Fixes 🐞
McpErrorin initialization middleware to prevent fallthrough by @jlowin in #3413fastmcp listandfastmcp callby @jlowin in #3409versionto components in FileSystemProvider by @martimfasantos in #3458refresh_expires_in=0as missing, fall back to 30-day default by @jlowin in #3514encodingparameter toFileResourceby @shulkx in #3580Docs 📚
Examples & Contrib 💡
Dependencies 📦
Configuration
📅 Schedule: (UTC)
🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.
♻ Rebasing: Whenever PR is behind base branch, or you tick the rebase/retry checkbox.
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