A vulnerability in Google’s Brotli data compression library, tracked as CVE-2026-111497 and dubbed Node2Shell, has led to security updates from Microsoft, the Node.js project and the maintainers of two Python packages.
Node.js and the Python packages were patched last week, and Microsoft followed on October 25 with fixes for .NET, Visual Studio and PowerShell. Bun, Envoy and Istio have also been updated.
Brotli is a popular choice for compressing data sent over the web, and its decoder is embedded in a long list of applications and libraries.
Described as an out-of-bounds write, the bug impacts Brotli 1.0.3 through 1.2.0. Google gave it a CVSS v4 score of 9.2, which puts it in the critical category. Brotli versions 1.0.10, 1.1.1 and 1.2.1 contain the fix.
The Node.js project said specially crafted input can push data beyond the limits of a buffer used by the decoder. The resulting memory corruption could cause the process to crash or leak memory contents, and could also allow an unauthenticated attacker to run arbitrary code.
Node.js credited the discovery to members of OpenAI Codex Security. According to OpenAI, the issue was uncovered during red-teaming work, after which the company notified the Brotli developers and the projects that rely on the library.
OpenAI noted that the fix predates the disclosure. “This root cause issue was actually fixed in the Brotli source code in February, but it wasn’t known at the time that it gave rise to a security vulnerability and there was no more recent release of Brotli,” the AI company said.
Code execution demonstrated on official Node.js image
Imperva has shown that it can be exploited for code execution on the official Node.js 24.22.0 image for Linux arm64. Its researchers sent the malicious data both in a server response retrieved by the targeted application and in a request body processed by Express 5 or body-parser 2.
“The proof did not succeed on every attempt. Our results establish code execution for the tested Linux arm64 build and application setups, and show how the fixed build handled the same inputs,” Imperva said. The security firm has not made its exploit public.
Attacks only work if malicious Brotli data reaches the decoder, for instance through a library that unpacks compressed content on the application’s behalf. “Any application that passes attacker-controlled data to an affected Google Brotli decoder may be exposed. This includes compressed HTTP request bodies, responses fetched from untrusted servers, and compressed files,” OpenAI’s Patch the Planet initiative said in its advisory.
No exploitation in the wild has been reported so far. A proof-of-concept exploit published on GitHub reportedly achieves code execution only against an intentionally weakened build, and some researchers argued the bug can only be used for denial-of-service (DoS) attacks.
Microsoft products and Python packages affected
Microsoft’s October 25 updates include .NET runtime versions 8.0.33, 9.0.22 and 10.0.14, along with .NET 11 Release Candidate 3. Visual Studio 2019, 2022 and 2026, as well as PowerShell 7.4, 7.5 and 7.6, have also been updated.
Microsoft has categorized CVE-2026-111497 as an elevation of privilege issue with a CVSS v3.1 base score of 8.1. It rates the flaw critical for .NET and Visual Studio and important for PowerShell, and its exploitability assessment is “Exploitation More Likely.”
In Python’s case, the vulnerable decoder is built into two PyPI packages, Brotli and brotlicffi. They have been patched with the release of versions 1.2.1 and 1.2.1.0, respectively.
As more affected software emerged, researchers began referring to the flaw as HTTP2Shell and Broccoli2Shell.
A public tracker of software that bundles its own copy of the Brotli decoder lists several projects that are still unpatched, including DuckDB, Apache Arrow, 7-Zip-zstd, p7zip and EDK II. Its maintainers say the list is incomplete, and that not every configuration of these projects necessarily exposes the vulnerable code.
Applying the updates also requires restarting affected services and rebuilding container images on top of a patched base, since processes that are already running keep using the vulnerable code.
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