CVE-2026-64684
RMCP: Custom HTTP headers leak to cross-origin redirect targets
- Published
- Updated
- Reserved
- Assigned by
- GitHub_M
Description
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.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_MCNA (assigner) | 3.1 | Medium6.8 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:N/A:N |
| NVDNVD · Awaiting Analysis | 3.1 | Medium6.8 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:N/A:N |
- EPSS (exploitation in 30 days)
- 0.50% · top 57% of all CVEs (6 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 6.8.
Weakness
Affected products
modelcontextprotocol · rust-sdk
- affected < 2.1.0
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- crates.iormcpGHSA-9g45-5xwm-f3wc (opens in a new tab)
References (4)
- https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-9g45-5xwm-f3wc (opens in a new tab)x_refsource_CONFIRM
- https://github.com/modelcontextprotocol/rust-sdk/pull/936 (opens in a new tab)x_refsource_MISC
- https://github.com/modelcontextprotocol/rust-sdk/commit/496902b9cf2c8a947454718da31829ae776b969b (opens in a new tab)x_refsource_MISC
- https://github.com/modelcontextprotocol/rust-sdk/releases/tag/rmcp-v2.1.0 (opens in a new tab)x_refsource_MISC
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-9g45-5xwm-f3wc (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2026-64684)Record last updated .