Microsoft Issues Out-of-Band .NET Security Updates Fixing Brotli Buffer Overflow and Other Flaws

Microsoft has released out-of-band security updates for .NET 10, .NET 9, and .NET 8 to address multiple vulnerabilities. The patches cover two newly identified issues and complete remediation for two additional flaws that received incomplete fixes during the October 13 monthly update cycle. One critical vulnerability, CVE-2026-111497, affects the Brotli compression library and can lead to information disclosure, denial of service, or privilege escalation when processing crafted compressed data. A second issue, CVE-2026-114148, enables local privilege escalation in Linux distribution packages for ASP.NET Core due to improper ownership handling. Microsoft also reissued fixes for remote code execution vulnerabilities CVE-2026-70197 and CVE-2026-102870. Organizations are advised to apply the updates immediately, including rebuilding and redistributing applications in container or embedded environments.

Security NEXTOctober 26, 2026Translated from Japanese

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Microsoft has published out-of-band security updates for the .NET application development platform to address multiple vulnerabilities. The company also completed remediation for issues that received insufficient fixes in the regular October security update.

On October 25, 2026, Microsoft released patches for .NET 10, .NET 9, and .NET 8. The updates resolve two newly discovered vulnerabilities and provide complete fixes for two additional flaws that were only partially addressed on October 13.

The first vulnerability, tracked as CVE-2026-111497, resides in the Brotli data compression library developed by Google. It is a buffer overflow flaw that occurs during decompression of specially crafted data. Successful exploitation can allow unauthenticated attackers to read memory contents, cause denial of service, or escalate privileges. The vulnerability affects applications that use the Brotli API to decompress externally supplied data, as well as ASP.NET Core request decompression and HttpClient response auto-decompression features when enabled. It carries a CVSS v3.1 base score of 8.1 and has been rated Critical by Microsoft. Workarounds include disabling Brotli processing.

The second vulnerability, CVE-2026-114148, affects Linux distribution packages for ASP.NET Core and related components. It stems from improper handling of file ownership information and can allow local attackers to modify files or escalate privileges. The issue is rated Important with a CVSS base score of 7.8.

Microsoft also reissued fixes for two remote code execution vulnerabilities, CVE-2026-70197 and CVE-2026-102870, that were incompletely patched during the regular October update. The company strongly recommends immediate installation of the updates. Applications that embed the runtime or run in container environments must be rebuilt and redistributed after the environment is updated.

Microsoft CVE-2026-111497 Brotli CVE-2026-114148 ASP.NET Core

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