Advisory details:
github_osv / GHSA-6jqx-86gh-f27w
| Advisory ID | github_osv/GHSA-6jqx-86gh-f27w |
| Aliases |
CVE-2026-55831
|
| Summary | Netty SPDY SETTINGS frame count materializes unbounded settings map ### 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 settings_count=262144 wire_bytes=2097164 approx_heap_delta=17692272 first_value=1 last_value=262144 ``` The `NETTY_SPDY_SETTINGS_COUNT_MAP_TRIGGERED` line means the harness decoded the crafted SETTINGS frame and observed all 262144 peer-selected IDs in the resulting settings map. The `wire_bytes=2097164`, `first_value=1`, and `last_value=262144` fields distinguish this from a setup failure: they show the exact oversized frame was accepted and fully materialized. ### Impact remote unauthenticated network peer that can speak SPDY/3.1 to a Netty pipeline containing `SpdyFrameCodec` can trigger resource-exhaustion denial of service. The required guards are satisfied by a complete valid SETTINGS frame using the expected SPDY version, a length of `4 + numSettings * 8`, and IDs within the accepted 24-bit range; the verified PoC uses `numSettings=262144` and `wire_bytes=2097164`. On that input, Netty materializes 262144 attacker-controlled entries in a TreeMap-backed `DefaultSpdySettingsFrame`, with local runs observing about 17-18 MiB of heap growth per decoded frame plus CPU work for ordered-map insertion. |
| Status | Published |
| Exploitability | 0.5 |
| Weighted Severity | 6.8 |
| Risk | 3.4 |
| Affected and Fixed Packages | Package Details |
| Introduced and Fixed Package Commit Patches | Package Commit Patches Details |
| System | Score | Found at |
|---|---|---|
| cvssv3.1 | 7.5 | https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/07/GHSA-6jqx-86gh-f27w/GHSA-6jqx-86gh-f27w.json |
| generic_textual | HIGH |
No EPSS data available for this advisory.
| Patch URL | |
|---|---|
| There are no known patches. | |
| Attack Vector (AV) | Attack Complexity (AC) | Privileges Required (PR) | User Interaction (UI) | Scope (S) | Confidentiality Impact (C) | Integrity Impact (I) | Availability Impact (A) |
|---|---|---|---|---|---|---|---|
network adjacent_network local physical |
low high |
none low high |
none required |
unchanged changed |
high low none |
high low none |
high low none |
There are no SSVC decisions available.