Affected: Homebrew: magic-wormhole

### Summary

permessage-brotli inflates each frame fully before checking maxMessagePayloadSize, so one 421-byte frame makes the server allocate about 545 MiB even with a 1 MiB message limit (brotli expands about 1,000,000:1). Any unauthenticated client can exhaust server memory this way on servers that enable permessage-brotli. This bypasses the GHSA-hxp9-w8x3-p566 fix.

### Details

In 26.7.1 the receive path passes the remaining `maxMessagePayloadSize` budget to `decompress_message_data(..., max_output_len=...)`. deflate and bzip2 stop at that budget. `PerMessageBrotli.decompress_message_data` (`compress_brotli.py`) instead calls `self._decompressor.process(data)` with no limit and compares the length afterwards, so the whole frame is inflated first.

The code comment and changelog say this is still "bounded on the wire by `maxFramePayloadSize`", but brotli reaches about 1,000,000:1 (841 bytes inflate to 1 GiB), so that bound means little. A 421-byte frame against a 1 MiB budget peaks at 545 MiB before the 1009 rejection.

An autobahn asyncio server on 127.0.0.1 accepting permessage-brotli, with `maxFramePayloadSize=64 KiB` and `maxMessagePayloadSize=1 MiB`, received one small brotli frame from an autobahn client and peaked at 545 MiB (baseline 28 MiB). A few concurrent connections can exhaust memory.

brotli ≥ 1.2.0 has `Decompressor.process(data, output_buffer_limit=N)`, so the backend can stop at `max_output_len` like deflate and bzip2 (and the extra's floor can be rais…

Affected: crossbario autobahn-python

Autobahn Python is a WebSocket and WAMP implementation for Python that supports Twisted and asyncio. From 26.7.1 until 26.10.1, PerMessageBrotli.decompress_message_data in compress_brotli.py calls the Brotli decompressor without an output limit and checks maxMessagePayloadSize only after a complete frame has been inflated. An unauthenticated WebSocket client can send a small, highly compressed frame that allocates hundreds of MiB before rejection, causing memory-exhaustion denial of service on servers that enable the opt-in permessage-brotli feature through the compress extra. Deflate and bzip2 already enforce the remaining output budget and are outside this residual vulnerability. This issue is fixed in version 26.10.1.