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CVE-2026-27124

24
FAUCET Score

CVE-2026-27124 identifies a high-severity Confused Deputy vulnerability in the FastMCP framework's OAuthProxy, impacting versions prior to 3.2.0 when using GitHub OAuth integration. The flaw arises from the proxy's failure to properly validate user consent during the OAuth callback, which, combined with GitHub's behavior of skipping consent for previously authorized clients, can lead to unauthorized actions. With a CVSS score of 8.2, this vulnerability carries a high integrity impact and is exploitable over the network with low complexity. There is currently no evidence of active exploitation, public exploit code, or significant community attention surrounding this issue.

Impacted Technologies

VendorProductVersion(s)CPE
< 3.2.0CPE matchmatch criteria
cpe:2.3:a:jlowin:fastmcp:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 4.0

8.2HIGH

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
PRESENT
Privileges Required
NONE
User Interaction
NONE
VS Confidentiality
NONE
VS Integrity
HIGH
VS Availability
NONE
SS Confidentiality
NONE
SS Integrity
NONE
SS Availability
NONE
Exploit Maturity
NOT_DEFINED
CvssVersion
4.0

Exploit Intelligence

EPSS Score
0.21%
Probability of exploitation in next 30 days
EPSS Percentile
11.0%
Percentile rank of EPSS score among Peer Group
As of 2026-07-26
Model: v2026.06.15
This CVE's current EPSS score of 0.0021 is in the 11th percentile among its peer group of 26,219 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.1 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (2)

pippatch availablevia ghsa
Product: fastmcpFixed in: 3.2.0
github_advisoryworkaround availablevia nvd_reference
View patch

Vendor Advisories (1)

pipGHSA-rww4-4w9c-7733high

FastMCP: Missing Consent Verification in OAuth Proxy Callback Facilitates Confused Deputy Vulnerabilities

Mar 31, 2026

References

github.com / PrefectHQ/fastmcp/security/advisories/GHSA-rww4-4w9c-7733
ExploitMitigationVendor Advisory