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Advisory record · GHSA-c9xm-49cp-xcr9

rmcp OAuth client fetches server-controlled resource_metadata URLs

CVSS 4.0, no score published

Published by the GitHub Advisory Database at 2 Oct 2026, 16:12 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
rmcpcrates.io<2.0.02.0.0
Identifiers
GHSA-c9xm-49cp-xcr9
Weakness (CWE)
CWE-918
Tags
Published
2 Oct 2026
Updated
2 Oct 2026

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

GHSA-c9xm-49cp-xcr9: The rmcp crate (Rust) before 2.0.0 accepts a resource_metadata URL from the WWW-Authenticate header sent by an MCP server and fetches it without same-origin or private-network checks. An attacker who controls or compromises an MCP server that the client connects to can make the client send a GET request to internal addresses such as localhost, private networks, or cloud metadata endpoints, which is a server-side request forgery. Upgrade to rmcp 2.0.0 or later; the source does not describe a workaround.

Written 3 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

ScoreRatingCVSSVectorSource
Not published None 4.0 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N GitHub Advisory Database
  • CISA KEV Not listed.
  • EPSS No score.

Timeline

  1. 31 Oct 2026, 14:24 UTC First seen by agentprime
  2. 31 Oct 2026, 14:24 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.