CVE-2026-13187 Overview
CVE-2026-13187 affects Progress Telerik UI for AJAX versions prior to v2026.2.708. The vulnerability resides in the DialogHandler component, where the provider type input can be tampered with by an attacker. This tampering alters dialog processing logic and can enable chained exploitation with other weaknesses in the application. The flaw is classified under [CWE-470: Use of Externally-Controlled Input to Select Classes or Code (Unsafe Reflection)]. Because Telerik UI for AJAX is widely embedded in enterprise ASP.NET web applications, successful exploitation can compromise confidentiality, integrity, and availability of the hosting application.
Critical Impact
Attackers can tamper with the DialogHandler provider type over the network without authentication, potentially enabling chained exploitation that impacts confidentiality, integrity, and availability.
Affected Products
- Progress Telerik UI for AJAX versions prior to v2026.2.708
- ASP.NET web applications embedding the vulnerable DialogHandler component
- Downstream products bundling Telerik UI for AJAX controls prior to the fixed release
Discovery Timeline
- 2026-07-22 - CVE-2026-13187 published to the National Vulnerability Database
- 2026-07-22 - Last updated in NVD database
Technical Details for CVE-2026-13187
Vulnerability Analysis
The vulnerability exists in the DialogHandler HTTP handler shipped with Telerik UI for AJAX. DialogHandler accepts a provider type value as part of its input. An attacker can modify this input to influence which provider class is loaded and instantiated during dialog processing. Because the type identifier is externally controlled and insufficiently constrained, the handler may resolve it to an unintended class. This behavior maps directly to unsafe reflection, where user-controlled input drives class selection. The processing path invoked by the tampered provider can deviate from the expected dialog workflow. Chained with additional Telerik or application-level weaknesses, this deviation can escalate into higher-impact outcomes such as arbitrary object instantiation or code execution paths.
Root Cause
The root cause is inadequate validation and allow-listing of the provider type identifier consumed by DialogHandler. The handler trusts client-supplied input to select a runtime type without enforcing a strict, closed set of permitted providers. This design falls under [CWE-470] and creates a reflection-driven attack surface.
Attack Vector
Exploitation occurs over the network against exposed Telerik UI for AJAX endpoints. The attack requires no authentication and no user interaction, but attack complexity is high because the attacker must craft input that survives partial validation and reaches the vulnerable code path. See the Telerik Security Advisory for CVE-2026-13187 for vendor guidance.
// No verified proof-of-concept is publicly available.
// The vulnerability is triggered by supplying a tampered
// provider type value to the DialogHandler endpoint.
// Refer to the Telerik advisory for technical specifics.
Detection Methods for CVE-2026-13187
Indicators of Compromise
- Unexpected HTTP requests to Telerik.Web.UI.DialogHandler.aspx containing unusual or non-standard provider type parameters
- Application logs showing reflection or type-load errors originating from Telerik.Web.UI assemblies
- Anomalous child processes spawned by the IIS worker process (w3wp.exe) hosting affected applications
Detection Strategies
- Inspect web server and WAF logs for requests to DialogHandler.aspx with modified query strings or POST bodies referencing unfamiliar type names
- Correlate dialog handler traffic with subsequent suspicious file writes, process launches, or outbound network activity from the web server
- Deploy signatures that flag serialized or reflection-oriented payloads targeting Telerik endpoints
Monitoring Recommendations
- Enable verbose logging on IIS and the ASP.NET application for DialogHandler requests, including request bodies where policy allows
- Alert on new or unusual .NET assemblies being loaded by the web application process
- Monitor for repeated 500-class responses from Telerik endpoints, which often accompany exploitation attempts
How to Mitigate CVE-2026-13187
Immediate Actions Required
- Upgrade Progress Telerik UI for AJAX to v2026.2.708 or later on all application servers
- Inventory ASP.NET applications and third-party products that bundle Telerik UI for AJAX to confirm coverage
- Restrict network exposure of DialogHandler.aspx where the control is not required by application functionality
Patch Information
Progress has addressed CVE-2026-13187 in Telerik UI for AJAX v2026.2.708. Administrators should apply the vendor-supplied release and redeploy affected applications. Full remediation details are available in the Telerik Security Advisory for CVE-2026-13187.
Workarounds
- Remove or disable the DialogHandler HTTP handler registration in web.config if the dialog functionality is not used by the application
- Apply WAF rules that reject requests to DialogHandler.aspx containing unexpected provider type values
- Limit access to Telerik endpoints through IP allow-listing or authenticated reverse proxies until patching completes
# Example: remove the DialogHandler mapping from web.config
# <system.webServer>
# <handlers>
# <remove name="Telerik_Web_UI_DialogHandler_aspx" />
# </handlers>
# </system.webServer>
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
