Machine-written summary
Summary written by Claude Haiku from the source advisory. Not reviewed by a person.
Fastmcp versions before 3.2.0 are affected. The OAuth proxy callback does not verify that the browser completing the flow has actually given consent, so when the identity provider skips its consent page for previously authorized clients (as GitHub does with GitHubProvider), an attacker who lures a logged-in victim to a captured authorization URL can obtain an authorization code and access token tied to the victim's account on the MCP server. Upgrade to fastmcp 3.2.0 or later.
Not analysed yet
We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.
Severity and exploitation
| Score | Rating | CVSS | Vector | Source |
|---|---|---|---|---|
| 8.2 | High | 4.0 | CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N | CNA (GitHub_M) |
- CISA KEV Not listed.
- EPSS 0.0021, the 11th percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.
Timeline
- 31 Oct 2026, 14:34 UTC First seen by agentprime
- 31 Oct 2026, 14:34 UTC Confirmed by OSV