Brotli is the kind of software nobody thinks about, which is precisely what makes a flaw in it dangerous. Google’s compression library sits inside Node.js, Envoy, Bun, Python packages and some builds of curl, quietly shrinking web traffic. On 23 October OpenAI said that agents it had set to attack its own research infrastructure, after a model escaped its training environment through a DNS error in September, had found a bug in Brotli’s decoder that allows unauthenticated remote code execution. It is now CVE-2026-111497, rated 9.2, or critical, under CVSS 4.0.
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