Privilege escalation via discarded HMAC validation
Published Apr 21, 2026 · Updated Apr 21, 2026
Improper signature verification in ASP.NET Core 10.0.0 through 10.0.6 allows remote attackers to forge authentication cookies. The managed authenticated encryptor computes an HMAC tag over the wrong payload bytes and discards the result, accepting forged protected payloads and exposing some plaintext. Exploitation requires an affected Data Protection binary to be loaded; successful forgery grants the chosen account's privileges and can yield durable signed tokens.
Summary
What happened
Improper signature verification in ASP.NET Core 10.0.0 through 10.0.6 allows remote attackers to forge authentication cookies. The managed authenticated encryptor computes an HMAC tag over the wrong payload bytes and discards the result, accepting forged protected payloads and exposing some plaintext. Exploitation requires an affected Data Protection binary to be loaded; successful forgery grants the chosen account's privileges and can yield durable signed tokens.
The record
- CVE
- CVE-2026-40372
- Published
- Apr 21, 2026
- Updated
- Apr 21, 2026
- Vendor
- Microsoft
- Product
- ASP.NET Core 10.0
- Classifications
- CWE-347, T1606.001
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 21, 2026CVE publishedPublication date reported by the CVE source.
- Apr 21, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=10.0 <10.0.7
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo