CVE-2026-55831 — Netty SPDY SETTINGS frame count materializes unbounded settings map

Affected: netty

Netty is a network application framework for development of protocol servers and clients. Prior to 4.1.136.Final and 4.2.16.Final, Netty's SPDY SETTINGS decoder accepts a peer-declared SETTINGS entry count up to the 24-bit frame-length limit and materializes every unique setting ID in `DefaultSpdySettingsFrame`, allowing a remote SPDY/3.1 peer to send a syntactically valid roughly 2 MiB SETTINGS frame that creates 262144 map entries and amplifies network input into heap growth and ordered-map insertion work. This issue is fixed in versions 4.1.136.Final and 4.2.16.Final.

GHSA-6jqx-86gh-f27w — Netty SPDY SETTINGS frame count materializes unbounded settings map

Affected: Maven: io.netty:netty-codec-http

### Summary Netty's SPDY SETTINGS decoder accepts a peer-declared SETTINGS entry count up to the 24-bit frame-length limit and materializes every unique setting ID in `DefaultSpdySettingsFrame` without an implementation-level count cap. A remote SPDY/3.1 peer can send one syntactically valid roughly 2 MiB SETTINGS frame that creates 262144 map entries, amplifying network input into heap growth and ordered-map insertion work.

### Details Inbound SPDY bytes enter `SpdyFrameCodec.decode()` and are passed directly to the frame decoder. The decoder reads the peer-controlled flags and 24-bit frame length from the common header, then accepts SETTINGS frames with only `length >= 4`. For SETTINGS payloads, it reads the peer-controlled `numSettings` field and validates only that the remaining payload is divisible into 8-byte entries and exactly matches that count. Each accepted entry then supplies an attacker-controlled 24-bit ID and value, and the normal delegate path forwards it into `spdySettingsFrame.setValue()`. The sink is `DefaultSpdySettingsFrame`: it backs settings with a `TreeMap`, checks only that IDs fit the SPDY 24-bit maximum, and inserts a new `Setting` for each previously unseen ID. There is no count budget between the wire-format count validation and the TreeMap insertion site.

### PoC [poc.zip](https://github.com/user-attachments/files/28445737/poc.zip)

run with ```bash bash ./poc/run.sh ```

expected output: ```text NETTY_SPDY_SETTINGS_COUNT_MAP_TRIGGERED setting…

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CVE-2026-55831 — Netty SPDY SETTINGS frame count materializes unbounded settings map

GHSA-6jqx-86gh-f27w — Netty SPDY SETTINGS frame count materializes unbounded settings map