AIKIDO-2026-301031
cesanta.mongoose is vulnerable to HTTP Request Smuggling
91
Critical Risk
This Affects:
cesanta.mongooseTL;DR
The built-in HTTP server detects the protocol version with an off-by-one comparison that never recognizes HTTP/1.0 requests. As a result the server accepts Transfer-Encoding: chunked on requests that a fronting HTTP/1.0 proxy frames using Content-Length. This inconsistent message-length interpretation lets externally supplied requests desync the proxy and server, smuggling a hidden request onto another client's connection. The fix corrects the version check so chunked encoding is rejected for HTTP/1.0.
Who does this affect?
You are affected if you are using a version that falls within the vulnerable range and you run the built-in HTTP server behind a reverse proxy that can interpret request boundaries differently.
Background info
cesanta.mongoose is vulnerable to HTTP Request Smuggling in versions 7.21 - 7.21.
How to fix this
Upgrade the cesanta.mongoose library to the patch version.
Links
GitHub Release
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