The flaw occurs in the DialogHandler component of Telerik UI for ASP.NET AJAX. A malicious actor can tamper with the provider type input supplied to the dialog request, bypassing normal server‑side validation. This allows the attacker to modify how the dialog is processed, creating a path for chained exploitation in the application. The weakness is an input validation failure, classified as CWE‑470. Attackers could leverage the manipulation to introduce unwanted behavior or, in the worst case, gain higher privileges within the affected application.

All releases of Progress Software’s Telerik UI for ASP.NET AJAX earlier than version 2026.2.708 are affected. Systems deploying any older build of the UI component that exposes the DialogHandler endpoint are susceptible to the provider type tampering vulnerability.

The CVSS score of 8.1 indicates a high severity, and the EPSS score of less than 1% suggests a low exploitation probability at the time of this analysis. The vulnerability is not listed in CISA’s KEV catalog, but the risk remains significant for organizations that have exposed the DialogHandler endpoint. The likely attack vector is through any HTTP request to the DialogHandler endpoint, either authenticated or unauthenticated, where an attacker can submit a crafted provider type value. As a result, the flaw could be combined with other weaknesses to enable more serious outcomes. The vulnerability’s practical exploitability depends on how exposed the endpoint is and whether the application implements additional safeguards.