Broccoli2shell: Everything You Need To Know About The Critical Brotli Decoder Vulnerability

What it is

CVE-2026-111497 (Broccoli2Shell, also called Node2Shell and HTTP2Shell) is an out-of-bounds write in the upstream Brotli C decoder. Khai Tran and Sylvie Mayer (OpenAI Codex Security) found and reported it. Matteo Collina and Antoine du Hamel fixed it for Node.js. Ron Masas (Imperva Red Team) demonstrated exploitation, and Aikido analyzed the impact on Python.

How it works

The decoder mishandles specially crafted compressed data during block processing and can write past allocated memory. An unauthenticated attacker who supplies malicious Brotli input can cause memory disclosure, crashes, or code execution with the privileges of the affected process. Researchers demonstrated exploitation against unpatched Node.js.

Preconditions / Affected

The application or one of its dependencies must decompress attacker-controlled Brotli data. That data can arrive in incoming HTTP requests, in responses fetched from external servers, in uploaded files, or in other untrusted content.

Some HTTP clients and frameworks decompress automatically when Brotli support is on, so an application can be exposed without mentioning Brotli in its own code. The page says to include indirect and transitive dependencies in the assessment.

Statically linked libraries and embedded copies of the decoder may also be affected. For these, the page says to check vendor advisories. End-of-life runtime branches should move to supported versions.

Wiz reports that 91% of cloud environments have vulnerable resources and 82% have publicly exposed Node.js instances.

What to do

• Upgrade Brotli libraries, Node.js, Python packages, Bun, Envoy Proxy and Istio to patched or later supported releases.
• Inventory VMs, Kubernetes clusters, containers, serverless functions and API gateways. Prioritize internet-facing services and workloads that handle untrusted compressed data.
• Update base images, lockfiles and bundled libraries, then rebuild and redeploy containers. Restart running processes and verify the patched components are actually loaded.
• If patching must wait, disable Brotli decompression or reject Brotli-encoded requests before they reach vulnerable components. Restrict untrusted compressed responses where feasible.
• Review WAF, application and network logs for suspicious Brotli traffic, unexpected crashes and anomalous process behavior.

Caveats

The page names no fixed version numbers, so check each vendor's advisory. It says the temporary mitigations may reduce exposure but do not replace patching. The post gives no detection signatures or indicators of compromise. Wiz customers can use a prebuilt query in the Wiz Threat Center.