Node2Shell Vulnerability Also Affects Python Brotli Packages

Summary

The article identifies CVE-2026-111497 in PyPI Brotli releases through 1.2.0 and brotlicffi releases bundling the 1.2.0 decoder. Fixes are Brotli 1.2.1 and brotlicffi 1.2.1.0; package advisory coverage was absent at publication.

Key points

Node2Shell is an out-of-bounds write in Brotli’s C decoder. The article says the flaw can crash processes, leak memory or potentially enable remote code execution; Python-side memory corruption and code execution were not tested.
The article’s source comparison found the upstream fix in Brotli 1.2.1; earlier PyPI Brotli releases through 1.2.0 are affected.
The authors identify brotlicffi releases bundling the 1.2.0 decoder, including 1.2.0.1 and 1.2.0.2, as affected, and report 1.2.1.0 as the fix. They did not diff or fuzz its source distributions.
An AddressSanitizer test of Brotli 1.2.0 with a crafted stream returned NEEDS_MORE_INPUT, while 1.2.1 rejected it with error −17, FORMAT_BLOCK_SWITCH.
Python services may encounter attacker-controlled Brotli data when HTTP clients decode responses or frameworks decode Brotli-compressed request bodies.
The article recommends upgrading to Brotli 1.2.1 or later and brotlicffi 1.2.1.0 or later; it reports that package advisory listings and scanners did not yet cover the affected PyPI packages.

Article Details

Attack Vectors: A crafted Brotli stream can trigger an invalid block-type switch in the vulnerable C decoder; the unchecked return value can leave the decoder running with corrupted state and cause an out-of-bounds write.
The vulnerable decoder may receive attacker-controlled compressed data in Brotli-encoded HTTP response bodies fetched by Python services or in inbound requests using Content-Encoding: br.
The article reports that the same decoder flaw is reachable in Node.js through fetch(), Express 5 / body-parser request bodies, and node:zlib. It says the flaw can crash a process, leak memory, or potentially enable remote code execution; Python-extension memory corruption and code execution were not tested.
Defensive Notes: Upgrade PyPI Brotli to 1.2.1 or later and brotlicffi to 1.2.1.0 or later; rebuild container images and wheels that bundle either package.
If an upgrade is not immediately possible, uninstall Brotli and brotlicffi, remove br from outbound Accept-Encoding headers, or reject inbound Content-Encoding: br.
Check installed versions in each environment. The article says pip-audit, Dependabot, and Safety did not flag these PyPI package exposures as of 23 October 2026.