Microsoft Security Advisory CVE-2026-40372 – ASP.NET Core Elevation of Privilege

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

9.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS

• CVE-2026-40372: 11.21% estimated exploitation activity in the next 30 days; percentile 95.96 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Executive Summary: A bug in Microsoft.AspNetCore.DataProtection 10.0.0-10.0.6 NuGet packages can give an attacker the opportunity to execute an Elevation of Privilege attack by forging authentication cookies, and also allows some protected payloads to be decrypted. If an attacker used forged payloads to authenticate as a privileged user during the vulnerable window, they may have induced the application to issue legitimately-signed tokens (session refresh, API key, password reset link, etc.) to themselves. Those tokens remain valid after upgrading to 10.0.7 unless the DataProtection key ring is rotated. This is comparable in capability to MS10-070, which exploited a similar padding-oracle condition in ASP.NET's legacy encryption infrastructure. Announcement Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/395 CVSS Details - Version: 3.1 - Severity: Important - Score: 9.1 - Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N - Weakness:…

Published by the source

23 Apr 2026, 14:55 UTC

Last modified by the source

24 Apr 2026, 19:59 UTC

Source last checked

26 Oct 2026, 17:04 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-9mv3-2cwr-p262

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# Patch Next advisory brief: CVE-2026-40372

Advisory: Microsoft Security Advisory CVE-2026-40372 – ASP.NET Core Elevation of Privilege
IDs: CVE-2026-40372, GHSA-9mv3-2cwr-p262
Record: https://patchnext.com/advisories/cve-2026-40372 (revision 1, source checked 26 Oct 2026, 17:04 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: microsoft.aspnetcore.dataprotection 10.0.7. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet microsoft.aspnetcore.dataprotection: affected >= 10.0.0, <= 10.0.6; fixed in 10.0.7

## Suggested inspection (read-only)
- NuGet microsoft.aspnetcore.dataprotection: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on microsoft.aspnetcore.dataprotection.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-9mv3-2cwr-p262 (GitHub-reviewed advisory GHSA-9mv3-2cwr-p262 lists affected ranges: NuGet microsoft.aspnetcore.dataprotection >=10.0.0 <=10.0.6)

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