Bug 2454826 (CVE-2026-27124)

Summary: CVE-2026-27124 FastMCP: FastMCP OAuthProxy: FastMCP OAuthProxy: Unauthorized actions due to improper consent validation in GitHub OAuth
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: abarbaro, alizardo, anthomas, dfreiber, drow, ehelms, ggainey, jburrell, jchui, jhe, jkoehler, juwatts, ktsao, lphiri, mbarnett, mhayden, mhulan, nboldt, nmoumoul, osousa, pcreech, psrna, rchan, rjohnson, sdoran, smallamp, tmalecek, vkumar
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: ---
Doc Text:
A flaw was found in FastMCP and FastMCP OAuthProxy. The OAuthProxy, used for GitHub OAuth authentication, does not properly validate a user's consent after receiving an authorization code from GitHub. This, combined with GitHub's behavior of skipping the consent page for previously authorized clients, creates a Confused Deputy vulnerability. This vulnerability could allow a remote attacker to perform unauthorized actions by exploiting the OAuth flow.
Story Points: ---
Clone Of: Environment:
Last Closed: Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-04-03 16:02:53 UTC
FastMCP is the standard framework for building MCP applications. Prior to version 3.2.0, 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. This issue has been patched in version 3.2.0.