Brotli Decoder Vulnerability Impacts Node.js, Bun, Python, .NET, and Other Software

Overview of CVE-2026-111497

A memory-corruption vulnerability in Google's Brotli compression decoder (tracked as CVE-2026-111497) affects multiple software ecosystems, including Node.js, Bun, Microsoft's .NET, Python packages, Envoy proxies, FFmpeg, ClickHouse, and Apache Arrow. The flaw arises from how the C code unpacks Brotli streams. If a program decodes attacker-controlled Brotli-compressed data, crafted payloads can cause a buffer overflow, potentially resulting in crashes, memory leaks, or remote code execution.

OpenAI's Codex Security team reported the issue, and Google assigned a CVSS score of 9.2 (critical). Other maintainers, including Red Hat and Microsoft, rate it between 8.1 (high) and important. According to available assessments, no in-the-wild exploitation has been publicly confirmed.

Affected Software and Exposure Vectors

Because various platforms bundle or reference their own copies of Google's decoder, they must be updated independently:

• Node.js and Bun: Exposed when built-in `fetch()` clients read Brotli responses (`Content-Encoding: br`) or when request-body parsers (such as Express 5) unpack incoming uploads.
• Python: Packages like `Brotli` and `brotlicffi` leave HTTP clients (`requests`, `httpx`, `urllib3`, `aiohttp`) vulnerable upon installation, even if an application never explicitly imports Brotli.
• .NET: Microsoft released out-of-band updates on October 25 for .NET 8, 9, and 10. Apps are exposed only if they use explicit Brotli APIs (`BrotliStream`) or enable automatic decompression.
• Other Systems: JFrog research identified vectors in FFmpeg (via libjxl metadata parsing), ClickHouse (handling HTTP requests, `.br` files, and Parquet data), and Apache Arrow.

Mitigation and Verification

Security advisories recommend the following verification and remediation steps:

• Update Runtimes and Libraries: Apply patches provided by vendors (such as updating Node.js, .NET runtimes, or Linux distribution packages). Restart running services and rebuild container images, as active processes retain the old decoder in memory.
• Disable Untrusted Decoding: Where updates are not yet available, reject incoming requests with `Content-Encoding: br` at the network edge, disable automatic client decompression, or uninstall unused Python Brotli bindings.
• Review Security Scanners: Automated dependency checkers may lag behind CVE records for Python packages or bundled libraries; administrators should manually verify installed versions.