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PYSEC-2026-4323
brotlicffibrotlicffibrotlicffiCVE-2026-111497 ("Node2Shell") is an out-of-bounds write (CWE-787) in Google's Brotli decoder (c/dec/decode.c). DecodeBlockTypeAndLength() returns an ambiguous value for an invalid block switch, and the fast decode path discards it (CWE-252, unchecked return value), so a crafted Brotli stream makes the decoder continue on corrupted state and write past the ring buffer. Upstream rates it CVSS 4.0 9.2 and classifies the impact as potential remote code execution.
The vulnerability is in Google's C library, not in Node.js specifically. The
PyPI Brotli package is Google's CPython binding and compiles the same
c/dec/decode.c that has the original vulnerability. All Brotli releases up to
and including 1.2.0 ship the vulnerable decoder; 1.2.1 contains the upstream
fix (commit 0ed4268a) and differs from 1.2.0 only in that fix plus a version
bump.
The decoder is reached whenever untrusted Brotli data is decompressed. With
brotlicffi installed, common HTTP clients decode Brotli responses automatically
(urllib3/requests, httpx with the brotli extra, aiohttp) and services that
accept Content-Encoding: br request bodies decode inbound data, so the flaw
is reachable from attacker-controlled input.
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The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability.
Active exploitation in the wild has been confirmed. Immediate patching or mitigation is required.
The exploit probability is critical. The vulnerability is very likely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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