CVE-2026-64684Network attack vector

Credential disclosure via cross-origin header replay

Published Sep 16, 2026 · Updated Sep 19, 2026

Information disclosure in Model Context Protocol Rust SDK before 2.1.0 allows remote attackers to steal custom HTTP credentials via redirects. StreamableHttpClientTransport applies caller-supplied custom_headers to requests made by a reqwest client whose default policy follows cross-origin 307 or 308 redirects. Exploitation requires a malicious or compromised MCP endpoint to redirect a client configured with custom authentication headers, exposing those credentials to the redirect target.

CVSS severity7.4
High
EPSS probability0.50%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Get started

Summary

What happened

Information disclosure in Model Context Protocol Rust SDK before 2.1.0 allows remote attackers to steal custom HTTP credentials via redirects. StreamableHttpClientTransport applies caller-supplied custom_headers to requests made by a reqwest client whose default policy follows cross-origin 307 or 308 redirects. Exploitation requires a malicious or compromised MCP endpoint to redirect a client configured with custom authentication headers, exposing those credentials to the redirect target.

The record

CVE
CVE-2026-64684
Published
Sep 16, 2026
Updated
Sep 19, 2026
Vendor
Model Context Protocol
Product
Rust SDK
Classifications
CWE-200, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 16, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 19, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=< 2.1.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Model Context Protocol · Rust SDKversion=< 2.1.0

Published CVSS scores

7.4GitHub Security AdvisoryCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:N/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.

Activity data is delayed. The latest report is Sep 28, 2026.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 22, 2026Sep 28, 2026
Latest reporting daySep 28, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-200Exposure of Sensitive Information to an Unauthorized Actor
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

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

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Get started to see how Hinoki identifies affected software and validates exploitability in your environment.

Get started