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VulnerabilityPublished Updated

Rmcp: Unbounded response body buffering

Affects rmcpSource GCVE Database

0

CVSS 6.5 Medium : upgrade to 3.9.0 when convenient.

Data as of 9 Nov 2026, 11:33 UTC

CVSS 3.1 base score
6.5Medium
How severe the flaw is on the 0–10 CVSS scale.
Patch
Available – fixed in 3.9.0
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

What to do

Upgrade rmcp to 3.9.0.

Affected software

ProductAffectedFixed in
crates.iormcppkg:cargo/rmcpOther threatsAffected
  • >=0.2.0 <3.9.0
Fixed in
  • 3.9.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade rmcp to version 3.9.0 or later, where this vulnerability is fixed by enforcing response body size limits and rejecting oversized bodies. If upgrading is not immediately possible, implement a custom StreamableHttpClient that enforces response body size limits or restrict connections to trusted MCP servers only. No other mitigations are indicated or required.

Description

Rmcp versions prior to 3.9.0 contain a vulnerability in their built-in Streamable HTTP clients where response bodies are buffered in memory without size limits. This affects the reqwest and Unix socket clients, causing them to fully buffer certain HTTP responses, including application/json POST responses and non-2xx error responses. A malicious or compromised MCP server can exploit this by sending an unending response body, leading to memory exhaustion and process termination. The issue is fixed in version 3.9.0 by imposing strict size limits on response bodies and rejecting oversized content.

References

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