CVE-2026-27124

Q: How do I fix CVE-2026-27124?

Upgrade fastmcp to 3.2.0 or later.

Q: Is CVE-2026-27124 being actively exploited?

Not that we know of. CVE-2026-27124 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.21% is the estimated probability that it will be exploited in the next 30 days. That is higher than 11% of all scored CVEs.

Q: How severe is CVE-2026-27124?

CVE-2026-27124 has a CVSS v3 base score of 6.1, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

Q: What does CVE-2026-27124 affect?

Published advisories record a fix for fastmcp (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

MEDIUM

6.1

CVSS v3

NVD

Description

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.

CWE-441

How to fix

Remediation Available

fastmcpNVD

Affected:< 3.2.0Fixed in:3.2.0CVE-2026-27124derived from NVD

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionRequired

ScopeChanged

Impact

ConfidentialityLow

IntegrityLow

AvailabilityNone

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Exploit Intelligence

0.21%probability of exploitation in 30 days

11thpercentile

Low risk: more likely to be exploited than 11% of all known CVEs.

References

Exploit1

github.com

Related Vulnerabilities

Other CWE-441 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2025-47269	High	8.3	43%	-	-
CVE-2019-3924	High	7.5	16%	-	Fix
CVE-2020-5412	Medium	6.5	10%	-	Fix
CVE-2019-3996	Medium	6.5	5.9%	-	-
CVE-2021-20042	Critical	9.8	2.7%	-	-
CVE-2019-1841	Medium	6.5	2.6%	-	Fix

Common questions

How do I fix CVE-2026-27124?

Upgrade fastmcp to 3.2.0 or later.

Is CVE-2026-27124 being actively exploited?

Not that we know of. CVE-2026-27124 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.21% is the estimated probability that it will be exploited in the next 30 days. That is higher than 11% of all scored CVEs.

How severe is CVE-2026-27124?

CVE-2026-27124 has a CVSS v3 base score of 6.1, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

What does CVE-2026-27124 affect?

Published advisories record a fix for fastmcp (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-07-24.