Brotli flaw that can let attackers run code reaches PAN-OS firewalls

A buffer overflow in Google’s Brotli decoder, CVE-2026-111497, can let an unauthenticated attacker crash a process, read its memory or run code by getting it to decompress crafted data. Node.js, Microsoft’s .NET, PHP’s Windows builds and Palo Alto’s PAN-OS bundle the decoder, and each has shipped fixes or scheduled them. Imperva ran code through the flaw on an official Node.js build. Sysdig says public exploits crash unpatched Node.js, and Palo Alto and Microsoft know of no attacks.

Brotli is a compression format that many HTTP-based applications use, Palo Alto notes. Node.js explains that the decoder treated an invalid block switch as a need for more input rather than an error. So it kept adding input to an eight-byte buffer and wrote past its end. Any application that decompresses Brotli data an attacker supplies can be hit, Node.js says. Imperva sent its data both in a request body and in a response the application fetched.

Palo Alto says PAN-OS 11.2.4 and later on PA-Series and VM-Series firewalls is exposed only when Brotli inspection and TLS decryption are both on. Brotli inspection is off by default. The management interface, Panorama and PAN-OS 11.1 and 10.2 aren’t affected. Microsoft says .NET decompresses Brotli only when an application opts in, and PHP says its Windows builds expose the flaw through cURL when automatic response decompression is on.

Imperva says its exploit ran code on the official Node.js 24.22.0 image for Linux arm64, though not on every attempt. Sysdig says Imperva hasn’t released it, and that public exploits crash unpatched Node.js. One team ran commands with its public exploit, Sysdig says, but needed a build that loads an unfixed system Brotli library and a predictable memory layout. Its blind remote attempts with address randomization on didn’t work. CISA recorded no exploitation on Oct 23, and Palo Alto and Microsoft say they know of no attacks.

Many projects ship their own copy of the decoder, so a system library update doesn’t fix them. Palo Alto says a Threat Prevention signature gives partial coverage. CISA rates the flaw not automatable but with total technical impact, and Microsoft rates exploitation more likely.