CVE-2026-42559: modelcontextprotocol rust-sdk Origin Validation Error
Vulnerability summary
CVE-2026-42559 is a high (CVSS 8.8) Origin Validation Error vulnerability in modelcontextprotocol rust-sdk. EPSS estimates a 0.24% chance of exploitation in the next 30 days, higher than 14.4% of scored vulnerabilities.
Advisory lineage
Upstream 0 · Downstream 0 · Related 1Timeline
- 14-05-2026PublishedVulnerability first disclosed.
- 14-05-2026Last modifiedVulnerability information updated.
Description
RMCP is an official Rust SDK for the Model Context Protocol. Prior to version 1.4.0, the rmcp crate's Streamable HTTP server transport (crates/rmcp/src/transport/streamable_http_server/) did not validate the incoming Host header. This allowed a malicious public website, via a DNS rebinding attack, to send authenticated requests to an MCP server running on the victim's loopback or private-network interface. This vulnerability is fixed in 1.4.0.
CVSS metrics
6 scores · 6 sources · 1 version- OSV · WolfiEcosystem advisory · calculated8.8HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- OSV · NpmEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:HDiffers
- OSV · ChainguardEcosystem advisory · calculated8.8HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- OSV · Crates.ioEcosystem advisory · calculated8.8HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- NVDNIST8.8HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
EPSS trend
Probability
0.24%
Chance of exploitation in the next 30 days
Percentile
14%
Versus all other CVEs
30-day change
+0.03 pp
From 0.21% on 19-09-2026
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root cause- CWE-346Origin Validation ErrorThe product does not properly verify that the source of data or communication is valid.
- CWE-350Reliance on Reverse DNS Resolution for a Security-Critical ActionThe product performs reverse DNS resolution on an IP address to obtain the hostname and make a security decision, but it does not properly ensure that the IP address is truly associated with the hostname.
Affected systems
Chainguard2 products
- nushell< 0.112.2-r3
- zed< 1.2.6-r1
Crates.Io2 products
- dynoxide-rs≥ 0.9.3, < 0.9.13
- rmcp< 1.4.0 | ≥ 0.0.0-0, < 1.4.0
Wolfi2 products
- nushell< 0.112.2-r3
- zed< 1.2.6-r1
Modelcontextprotocol1 product
- rust-sdk< 1.4.0
Npm1 product
- dynoxide≥ 0.9.3, < 0.9.13
5 vendors · 8 products
References
17 links- github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-89vp-x53w-74fxX Refsource CONFIRMAdvisoryWEB
- github.com/modelcontextprotocol/rust-sdk/commit/8e22aa2de28df5a285eed87c11cd89bf15fa90d3X Refsource MISCFIXWEB
- github.com/nubo-db/dynoxidePACKAGE
Show all 17 references
- crates.io/crates/dynoxide-rsPACKAGE
- crates.io/crates/rmcpPACKAGE