RMCP Streamable HTTP Server Transport Vulnerability
- Severity
- HIGH
- Affected component
- rmcp streamable http server transport (cargo)
- Patched version
- Not yet available
An unauthenticated remote attacker can reportedly leak one entry per HTTP request out of the in-memory session table of `LocalSessionManager` in the rmcp Streamable HTTP server transport leading to a remote denial-of-service.
What happened
An unauthenticated permanent session-table leak in rmcp Streamable HTTP server transport has been reported. This vulnerability allows an attacker to leak one entry per HTTP request out of the in-memory session table of `LocalSessionManager` leading to a remote denial-of-service. This issue was first flagged on 2026-09-16T22:13:34+00:00 and is currently under investigation.
To assess your exposure, check if your system uses the rmcp Streamable HTTP server transport. Since no authoritative version range has been published yet, it is recommended to upgrade to a version of `rmcp` that patches this vulnerability and monitor for any unusual memory usage.
What to do about it
- Upgrade to a version of `rmcp` that patches this vulnerability.
- Monitor for any unusual memory usage.
- No official fix has been published yet. Monitor the sources below for updates.
How 0Day would have caught this
rmcp streamable http server transport is anywhere in your dependency tree, the engineers who own the affected repositories get a push alert the moment it is flagged — no manual audit to remember to run.Read how this differs from waiting on a scanner to catch a known advisory, or see the exact, read-only access 0Day needs to do this for an organization.
Frequently asked questions
Am I affected?
You may be affected if your system uses the rmcp Streamable HTTP server transport. Since no authoritative version range has been published yet, it is recommended to check for updates and apply any available patches.
What should I do right now?
Upgrade to a version of `rmcp` that patches this vulnerability and monitor for any unusual memory usage. Since no official fix has been published yet, continue to monitor the sources for updates.
Where can I find more information?
Consult the primary source at https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-9pj6-vhgr-3mwh for the latest information and updates.