Cve-2026-40372 — CraftedSignal Threat Feedhttps://feed.craftedsignal.io/tags/cve-2026-40372/Trending threats, MITRE ATT&CK coverage, and detection metadata — refreshed continuously.Hugoenhello@craftedsignal.iohello@craftedsignal.ioWed, 22 Apr 2026 12:00:00 +0000ASP.NET Core Improper Signature Verification Vulnerability (CVE-2026-40372)https://feed.craftedsignal.io/briefs/2026-04-aspnet-privesc/Wed, 22 Apr 2026 12:00:00 +0000hello@craftedsignal.iohttps://feed.craftedsignal.io/briefs/2026-04-aspnet-privesc/CVE-2026-40372 is a critical vulnerability in ASP.NET Core stemming from improper cryptographic signature verification, potentially enabling unauthorized attackers to achieve network-based privilege escalation.CVE-2026-40372 describes a critical vulnerability affecting ASP.NET Core applications. This flaw arises from the improper verification of cryptographic signatures, creating an avenue for unauthorized attackers to elevate their privileges within a network. Successful exploitation of this vulnerability could grant attackers significant control over affected systems. According to the NVD, the CVE was published on April 21, 2026. Given the severity of privilege escalation and the potential for widespread impact on ASP.NET Core deployments, this vulnerability poses a significant risk and demands immediate attention from security teams. The vulnerability is referenced by Microsoft in their advisory related to CVE-2026-40372.

Attack Chain

  1. Attacker identifies an ASP.NET Core application vulnerable to CVE-2026-40372.
  2. The attacker crafts a malicious request containing a tampered cryptographic signature.
  3. The vulnerable ASP.NET Core application fails to properly verify the cryptographic signature due to the flaw described in CVE-2026-40372.
  4. The application processes the malicious request as if it were legitimate, bypassing authentication or authorization checks.
  5. The attacker leverages the bypassed checks to gain access to sensitive functions or data.
  6. Attacker escalates privileges within the ASP.NET Core application context.
  7. The attacker leverages the elevated privileges to perform unauthorized actions, such as modifying data, executing code, or accessing restricted resources.
  8. The attacker achieves full control of the compromised ASP.NET Core application and potentially the underlying server, depending on application permissions and configuration.

Impact

Successful exploitation of CVE-2026-40372 can lead to complete compromise of affected ASP.NET Core applications. An attacker gaining elevated privileges can modify sensitive data, execute arbitrary code, or disrupt services. Given the widespread use of ASP.NET Core in web applications across various sectors, the potential impact is substantial. The vulnerability’s critical severity (CVSS 9.1) highlights the high risk it poses to organizations relying on ASP.NET Core.

Recommendation

  • Apply the security update provided by Microsoft to address CVE-2026-40372 as detailed in the Microsoft advisory [https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40372].
  • Deploy the Sigma rule “Detect Suspicious ASP.NET Core Request” to identify potential exploitation attempts in web server logs.
  • Review ASP.NET Core application configurations to minimize the potential impact of privilege escalation.
  • Enable web server logging to capture detailed information about incoming requests, aiding in the detection and investigation of exploitation attempts (webserver category).
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