CVE-2025-69196Public exploitNetwork attack vector

Cross-server access via unbound OAuth tokens

Published Mar 16, 2026 · Updated Mar 16, 2026

Incorrect authorization in FastMCP before 2.14.2 allows remote attackers to reuse stolen OAuth tokens across MCP servers. OAuthProxy initializes JWTIssuer with base_url as a shared issuer and audience and ignores the client-supplied resource when binding access and refresh tokens. Exploitation requires a victim to complete an OAuth flow with a malicious MCP server advertising the same authorization server, after which the attacker can access tools and resources exposed by benign servers sharing that server.

CVSS severity7.4
High
EPSS probability0.36%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Incorrect authorization in FastMCP before 2.14.2 allows remote attackers to reuse stolen OAuth tokens across MCP servers. OAuthProxy initializes JWTIssuer with base_url as a shared issuer and audience and ignores the client-supplied resource when binding access and refresh tokens. Exploitation requires a victim to complete an OAuth flow with a malicious MCP server advertising the same authorization server, after which the attacker can access tools and resources exposed by benign servers sharing that server.

The record

CVE
CVE-2025-69196
Published
Mar 16, 2026
Updated
Mar 16, 2026
Vendor
Prefect Technologies, Inc.
Product
FastMCP
Classifications
CWE-863, T1550.001, T1528
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 16, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 16, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 2.14.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Prefect Technologies, Inc. · FastMCPversion=< 2.14.2

Published CVSS scores

7.4GitHub, Inc.CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
7.4redhat-SADPCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-863Incorrect Authorization
T1550.001Application Access Token
T1528Steal Application Access Token

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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