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CVE-2026-40372 is an elevation-of-privilege vulnerability in ASP.NET Core Data Protection affecting Microsoft.AspNetCore.DataProtection NuGet package versions 10.0.0 through 10.0.6. The flaw resides in the managed authenticated encryptor, where HMAC validation can be performed incorrectly because the validation tag is computed over the wrong bytes of the payload and the computed hash may then be discarded. This breaks integrity verification for Data Protection payloads and allows forged protected data to be accepted as valid. In practical terms, an unauthenticated remote attacker can abuse the flaw to forge authentication cookies and tamper with other protected application artifacts, and some protected payloads may also be decrypted. Reported affected artifacts include authentication cookies, antiforgery tokens, TempData, and OpenID Connect state. The issue was fixed in Microsoft.AspNetCore.DataProtection 10.0.7.
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An elevation-of-privilege vulnerability in .NET affecting versions 10.0.0 through 10.0.6, caused by forged authentication cookies and serious enough to prompt a follow-up update.
A critical privilege escalation vulnerability in ASP.NET Core Data Protection cryptographic APIs caused by a regression in Microsoft.AspNetCore.DataProtection NuGet packages that incorrectly compute HMAC validation tags, potentially allowing attackers to forge payloads, bypass authenticity checks, decrypt protected payloads, and gain elevated privileges.
A high-impact ASP.NET Core privilege-escalation vulnerability in the Data Protection cryptographic APIs caused by improper verification of a cryptographic signature, enabling forged protected payloads, disclosure/modification of data, and potential SYSTEM-level privilege escalation under specific conditions.
A high-severity ASP.NET Core DataProtection vulnerability caused by faulty verification of cryptographic signatures, allowing unauthenticated attackers to forge authentication payloads and gain SYSTEM privileges on affected Linux or macOS systems.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.