Bug 2535732 (CVE-2026-64684)

Summary: CVE-2026-64684 rmcp: RMCP: Sensitive HTTP headers leaked during cross-origin redirects
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the `rmcp` component. This vulnerability allows a remote attacker to disclose sensitive information. When the `rmcp` crate's HTTP client processes a redirect to a different web address (cross-origin redirect) from a malicious or compromised Model Context Protocol (MCP) endpoint, it can inadvertently replay custom HTTP headers, such as API keys or authentication tokens, to the new, untrusted destination. This enables an attacker to capture and potentially reuse these sensitive credentials.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2535856, 2535857    
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Description OSIDB Bzimport 2026-09-16 21:29:51 UTC 
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.