Microsoft shipped .NET updates out of band on Saturday (Oct 25) for CVE-2026-111497, an out-of-bounds write in the Brotli decoder bundled with .NET. The .NET advisory scores it 8.1 and MSRC rates it Critical for .NET, and Microsoft says exploitation is more likely, with no exploitation reported as of the 25th.
The patched runtimes are 8.0.33, 9.0.22 and 10.0.14. Anything below those is still exposed, and .NET Framework is not affected, so older Framework servers can sit this one out. The same release also fixes CVE-2026-114148, a file-ownership problem in .NET tarballs on Linux, and it re-does two October 13 fixes that had not fully landed (CVE-2026-70197 and CVE-2026-102870).
A few things that decide how urgent this is on a given box:
Exposure needs an app that decompresses Brotli data it does not control, through ASP.NET Core request decompression, HttpClient automatic decompression, or the System.IO.Compression Brotli APIs. Neither decompression path is on by default, so a patched-later queue is defensible for internal apps that never enable them, while internet-facing ASP.NET Core goes first.
Updating the shared runtime does nothing for self-contained apps because they carry their own copy of the runtime, and those need a rebuild and redeploy. Framework-dependent apps pick the fix up from the runtime update, though the processes still need a restart, and on IIS that means updating the ASP.NET Core Hosting Bundle rather than only the runtime.
PowerShell is in scope as well, with fixes in 7.4.22, 7.5.13 and 7.6.9, which matters on admin workstations that never run a .NET app. Anyone on Azure App Service with built-in .NET images on Linux gets the platform update from Microsoft; the rollout had finished for the Latest channel and was still going out to Standard as of Oct 26.
`dotnet --list-runtimes` gives a quick inventory per machine. Microsoft's announcement is here: https://devblogs.microsoft.com/dotnet/dotnet-october-2026-oob-security-updates/