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VulnerabilityPublished Updated

Mcpm: FastMCP Auth Integration Allows for Confused Deputy Account Takeover

Affects mcpmSource GCVE Database

0

CVSS 7.3 High : upgrade to 2.12.0 soon.

Data as of 22 Oct 2026, 17:29 UTC

CVSS 4.0 base score
7.3High
How severe the flaw is on the 0–10 CVSS scale.
Patch
Available – fixed in 2.12.0
CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

What to do

Upgrade mcpm to 2.12.0.

Affected software

ProductAffectedFixed in
Homebrewmcpmpkg:brew/mcpmOther threatsAffected
  • >=2.1.0 <2.12.0
Fixed in
  • 2.12.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A patch is available for this vulnerability. Users should apply the official fix provided by the FastMCP vendor. Until patched, consider reviewing the authentication integration configuration to avoid using static client registrations shared across multiple MCP clients or implement additional validation to prevent confused deputy scenarios.

Description

FastMCP's authentication integration with Entra ID allows the MCP server to act both as an OAuth client and authorization server. Due to Entra ID's lack of Dynamic Client Registration support, the FastMCP server uses a static app registration for authorization. After a user consents to this static client, Entra ID sets a persistent authorization cookie. An attacker controlling their own MCP client can exploit this by initiating authorization flows that reuse the victim's consented static client ID, potentially leading to confused deputy account takeover.

References

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