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CVE-2026-13181 – Remote Code Execution via Unsafe Type Resolution – Progress Telerik UI for ASP.N…

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Summary

CVE-2026-13181 is a high-severity vulnerability in Progress Telerik UI for ASP.NET AJAX affecting all versions from 2010.1.309 through 2026.2.519, fixed in v2026.2.708. The flaw arises from the RadAsyncUpload component resolving server-side .NET types from attacker-controlled upload metadata — specifically the AsyncUploadTypeName parameter — without adequate validation, enabling unauthenticated remote code execution. The vulnerability is classified under CWE-470 (Use of Externally-Controlled Input to Select Classes or Code) and carries a CVSS v3.1 base score of 8.1 (HIGH).

Technical details

  • Root cause: The RadAsyncUpload handler (Telerik.Web.UI.WebResource.axd) processes type names supplied within forged upload metadata. The AsyncUploadTypeName field is resolved to a .NET type without sufficient validation, enabling an attacker to influence object instantiation on the server — an object injection pattern classified as CWE-470 / CAPEC-586.
  • Trigger conditions: The application must have the RadAsyncUpload control in active use and the async upload handler must not have been explicitly disabled via the Telerik.Web.DisableAsyncUploadHandler configuration key.
  • Attack vector: Network-delivered over HTTP/HTTPS; no authentication required, no user interaction required. The handler endpoint is accessible to unauthenticated internet users on affected deployments.
  • Impact: Full remote code execution on the server — confidentiality, integrity, and availability are all rated HIGH (C:H/I:H/A:H). Successful exploitation can result in complete server compromise.

Affected software

  • Progress Telerik UI for ASP.NET AJAX versions 2010.1.309 through 2026.2.519 (inclusive) — all versions prior to the 2026 Q2 SP1 release

Severity

  • CVSS v3.1 Base Score: 8.1 (HIGH)
  • Vector string: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Note: The High Attack Complexity (AC:H) reflects the prerequisite that RadAsyncUpload must be actively configured in the application. It does not reduce severity for environments meeting that condition.

Mitigation and recommended actions

  • Immediate — upgrade: Apply Progress Telerik UI for ASP.NET AJAX v2026.2.708 (2026 Q2 SP1) or later. This release addresses the unsafe type resolution in AsyncUploadTypeName handling.
  • If immediate upgrade is not feasible — workarounds:
    • Disable the async upload handler entirely by setting Telerik.Web.DisableAsyncUploadHandler to true in web.config. This blocks the vulnerable code path if RadAsyncUpload functionality is not required.
    • Configure strong, manually generated machine keys in IIS using HMACSHA256 validation to reduce the effectiveness of forged metadata. Do not rely on auto-generated keys.
    • Review and restrict network access to the Telerik.Web.UI.WebResource.axd handler endpoint where possible.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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