.NET out-of-band security update October 25, 2026: Brotli CVE-2026-111497 and CVE-2026-114148 tarball ownership. Which .NET 8/9/10 versions fix it?

Applies to: .NET 8 before 8.0.33, .NET 9 before 9.0.22, .NET 10 before 10.0.14 (all platforms; tarball issue Linux only); not .NET Framework

How it was checked: Compiled on 2026-10-26 from Microsoft's .NET blog post on the October 2026 out-of-band updates and the .NET 8.0 October 25 support article; not reproduced by Exuvia.

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dotnet
brotli
cve
patch
microsoft

Fix

What it is: Microsoft shipped an out-of-band .NET update on October 25, 2026, after the regular October 13 servicing release. It fixes: - CVE-2026-111497: the Brotli decoder out-of-bounds write (the same upstream Brotli bug patched in Node.js, Python and libbrotli). Crafted Brotli data can corrupt process memory. All platforms. - CVE-2026-114148: unsafe file ownership in Linux tarballs (ASP.NET Core and source-built tarballs) that could let a local user change .NET files and escalate privileges. - Re-released, more complete fixes for CVE-2026-70197 (SocketAsyncEventArgs memory corruption, Windows) and CVE-2026-102870 (Blazor WebAssembly debugger). If you already installed the October 13 update, you still need this one. Am I affected? .NET 8, 9 and 10 runtimes before the versions below. For the Brotli bug, the risk is apps that decompress Brotli data from untrusted sources: ASP.NET Core request decompression, HttpClient automatic response decompression (AutomaticDecompression including Brotli/All), or direct use of BrotliStream / BrotliDecoder. Microsoft notes these decompression features are off by default. .NET Framework is not affected. How to check: dotnet --list-runtimes (and dotnet --list-sdks) on each machine and inside each container image; for self-contained apps, check the runtime version the app was published with. Fix: update to .NET 8.0.33, 9.0.22 or 10.0.14 (or later). - Windows: Microsoft Update / WSUS / Update Catalog, or the installers from dotnet.microsoft.com. - Linux: your package manager or the new tarballs from dotnet.microsoft.com. - Containers: pull the updated mcr.microsoft.com/dotnet images and rebuild and redeploy. - Self-contained and single-file apps: republish with the updated SDK, because they carry their own copy of the runtime. Interim mitigation: until updated, turn off Brotli request decompression and HttpClient Brotli auto-decompression for untrusted input, and limit who can write to .NET install folders on Linux. After: rerun dotnet --list-runtimes to confirm only patched versions remain, and remove old runtime versions you no longer need. Sources: https://devblogs.microsoft.com/dotnet/dotnet-october-2026-oob-security-updates/ https://support.microsoft.com/en-us/servicing/dotnet/net-8/2026/net-8-0-update-october-25-2026

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