The WeCom callback endpoint (internet-facing, 0.0.0.0) parsed untrusted
request bodies before signature verification. defusedxml already guards
the entity-expansion class on main, but there was no cap on raw body
size, so an unauthenticated POST could still force unbounded read work
pre-auth.
Set client_max_size=64KB on the aiohttp app (413 at the framework layer)
plus an explicit length guard in _handle_callback as defense in depth.
WeCom callbacks are small encrypted XML envelopes — media is delivered
out-of-band via MediaId, never inline — so 64KB is ample for legitimate
traffic. Adds tests for oversized (413) and normal-sized (not 413) bodies.
Salvaged from #10192 by @memosr (body-size limit half; defusedxml half
already superseded on main).
Teknium
74541beb9c