A critical buffer overflow in Google's Brotli compression decoder, tracked as CVE-2026-111497 and nicknamed HTTP2Shell, Node2Shell and Broccoli2Shell, can crash processes, leak memory or allow remote code execution in software that decompresses attacker-controlled Brotli data, BleepingComputer reported Monday¹.

The flaw is in the C decoder library shipped with Node.js and used elsewhere, and it affects Brotli 1.0.3 through 1.0.9, 1.1.0 and 1.2.0¹.

BleepingComputer said the bug was first identified in Node.js, then traced to the shared Brotli decoder, which is why it has several names¹. HTTP2Shell refers to HTTP clients and servers, but the issue is not limited to HTTP/2¹.

Besides Node.js, potentially affected software includes Python HTTP clients such as urllib3 with Brotli, requests, httpx and aiohttp with speedups when they use a vulnerable decoder, according to the report¹.

Microsoft issued an emergency.NET update on Sunday, warning that successful exploitation can escalate privileges on systems with a vulnerable.NET version¹.

Node.js, in an advisory quoted by BleepingComputer, said an invalid block switch was treated as a need for more input rather than a format error, so the streaming decoder kept appending bytes to an eight-byte buffer¹.

An attacker would need an application to decompress malicious data, for example by serving a compressed HTTP response to a client fetching a URL, or by sending a compressed request to a server¹. Node.js says that can crash the process, expose memory and enable remote code execution¹. Imperva, cited by BleepingComputer, said exploitation of CVE-2026-111497 can lead to remote code execution¹.

Upstream Brotli fixes were first committed in February, with Node.js and Google releasing stable user fixes on Oct. 21 and public disclosure the next day, the report said¹. PyPI packages with fixes arrived Oct. 23¹.

Patched versions listed are Google Brotli 1.0.10, 1.1.1 and 1.2.1; Node.js 22.23.4, 24.22.1 and 26.12.1; Python Brotli 1.2.1; and Python brotlicffi 1.2.1.0¹.

Proof-of-concept exploits have been published, but BleepingComputer said there were no reports of malicious exploitation in the wild¹. After updating, processes must be restarted and container images rebuilt¹. A tracking site cited in the report warned that updating a system Brotli library does not fix Node.js or other apps that bundle their own copy, and that blocking inbound Brotli still leaves a malicious HTTP-response path¹.