CVE-2026-63127 RMCP - Authentication Bypass

RMCP Rust SDK < 2.0.0 contains an OAuth authorization bypass caused by omission of RFC 9728 resource field validation in ResourceServerMetadata, letting malicious MCP servers impersonate victims by capturing access tokens, exploit requires victim to complete authorization flow.

CVSS base score 8.2 /10
High
CISA KEV
Not listed
Public exploit
None known
Authentication
Not required
EPSS
0.20% chance of exploitation in 30 days
View the NVD record ↗

Details

Type
Authentication Bypass
Impact
Broken Authentication
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N
Published
16 September 2026
Updated
15 October 2026
Weakness
CWE-345

Vendor fix

Upgrade to version 2.0.0 or later.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

References

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