Model Context Protocol RMCP SDK up to 2.0.x StreamableHttpClientTransport streamable_http_client.rs apply_custom_headers information disclosure

CVSS Meta Temp Score
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CTI Interest Score
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5.9$0-$5k0.44+

Summaryinfo

A vulnerability was found in Model Context Protocol RMCP SDK up to 2.0.x. It has been classified as problematic. This affects the function apply_custom_headers of the file crates/rmcp/src/transport/common/reqwest/streamable_http_client.rs of the component StreamableHttpClientTransport. This manipulation causes information disclosure. This vulnerability appears as CVE-2026-64684. The attack may be initiated remotely. There is no available exploit. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability classified as problematic was found in Model Context Protocol RMCP SDK up to 2.0.x. Affected by this vulnerability is the function apply_custom_headers of the file crates/rmcp/src/transport/common/reqwest/streamable_http_client.rs of the component StreamableHttpClientTransport. The manipulation with an unknown input leads to a information disclosure vulnerability. The CWE definition for the vulnerability is CWE-200. The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information. As an impact it is known to affect confidentiality. The summary by CVE is:

RMCP is an official Rust SDK for the Model Context Protocol. Prior to 2.1.0, the rmcp crate's StreamableHttpClientTransport in crates/rmcp/src/transport/common/reqwest/streamable_http_client.rs builds its default_http_client with reqwest's automatic redirect policy and applies caller-supplied values from StreamableHttpClientTransportConfig.custom_headers without marking them as sensitive. When a malicious or compromised MCP endpoint returns a cross-origin 307 or 308 redirect, reqwest follows the redirect and apply_custom_headers causes custom API keys or authentication tokens to be replayed to the new origin, where an attacker can capture and reuse them. The separate auth_header path is not affected because it uses the standard Authorization header, which reqwest strips on cross-origin redirects. This issue is fixed in version 2.1.0.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-64684 since 07/20/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1592 according to MITRE ATT&CK.

Upgrading to version 2.1.0 eliminates this vulnerability.

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Vendor

Name

Version

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 6.0
VulDB Meta Temp Score: 5.9

VulDB Base Score: 5.3
VulDB Temp Score: 5.1
VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA Base Score: 6.8
CNA Vector (GitHub_M): 🔒

CVSSv2info

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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Information disclosure
CWE: CWE-200 / CWE-284 / CWE-266
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: RMCP SDK 2.1.0

Timelineinfo

07/20/2026 CVE reserved
09/16/2026 +58 days Advisory disclosed
09/16/2026 +0 days VulDB entry created
09/16/2026 +0 days VulDB entry last update

Sourcesinfo

Advisory: github.com
Status: Confirmed

CVE: CVE-2026-64684 (🔒)
GCVE (CVE): GCVE-0-2026-64684
GCVE (VulDB): GCVE-100-406243

Entryinfo

Created: 09/16/2026 23:51
Changes: 09/16/2026 23:51 (66)
Complete: 🔍
Cache ID: 216::103

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