CVE-2026-13189 Overview
CVE-2026-13189 is a path traversal vulnerability in Progress® Telerik® UI for AJAX affecting versions prior to 2026.2.708. The flaw resides in the spell check handler, which insufficiently validates the dictionaryLanguage parameter. Attackers can manipulate this parameter to influence server-side file path resolution and trigger unintended server-side requests. The weakness is classified under [CWE-36] Absolute Path Traversal. Exploitation requires no authentication and can be performed remotely over the network, exposing confidential file contents on affected servers.
Critical Impact
Unauthenticated remote attackers can influence server-side file path resolution through the spell check handler, potentially disclosing sensitive files hosted by the affected ASP.NET AJAX application.
Affected Products
- Progress Telerik UI for AJAX versions prior to 2026.2.708
- ASP.NET AJAX applications embedding the Telerik RadSpell component
- Web applications exposing the Telerik spell check handler endpoint
Discovery Timeline
- 2026-07-22 - CVE-2026-13189 published to NVD
- 2026-07-22 - Last updated in NVD database
Technical Details for CVE-2026-13189
Vulnerability Analysis
The vulnerability affects the Telerik UI for AJAX spell check handler. The handler accepts a language parameter that selects the dictionary file used for spell checking. The handler does not sufficiently validate this parameter before using it in server-side file path resolution. An attacker can supply crafted values that escape the intended dictionary directory. This allows the server to resolve paths outside the expected scope and issue unintended server-side requests. The confidentiality impact is significant because file contents referenced during dictionary loading may be returned or otherwise exposed to the attacker.
Root Cause
The root cause is improper validation of the dictionaryLanguage parameter passed to the spell check handler. The component treats attacker-supplied input as a trusted path component. Because [CWE-36] Absolute Path Traversal applies, the input can specify absolute or traversal sequences that resolve to arbitrary locations. No canonicalization or allow-list check restricts the parameter to legitimate dictionary identifiers.
Attack Vector
The attack is delivered over the network without authentication or user interaction. An attacker sends an HTTP request to the Telerik spell check handler with a manipulated dictionaryLanguage value. The server resolves the manipulated path and performs file access or issues server-side requests on behalf of the attacker. Refer to the Telerik Security Advisory CVE-2026-13189 for vendor-provided technical details. No verified public exploit code is available at the time of publication.
Detection Methods for CVE-2026-13189
Indicators of Compromise
- HTTP requests to the Telerik spell check handler containing traversal sequences such as ../, encoded variants (%2e%2e%2f), or absolute paths in the dictionaryLanguage parameter
- Unexpected outbound connections originating from the web server process shortly after spell check handler requests
- Web server access logs showing anomalous language parameter values that do not match configured dictionary identifiers
Detection Strategies
- Inspect IIS or ASP.NET logs for requests targeting Telerik dialog and spell check endpoints with non-standard dictionaryLanguage values
- Deploy WAF signatures that detect path traversal patterns in query strings and POST bodies destined for Telerik handlers
- Correlate web application requests with file system access events on the hosting server to identify reads outside the dictionary directory
Monitoring Recommendations
- Enable verbose logging on the Telerik spell check handler and forward logs to a centralized analytics platform
- Alert on any handler invocation that references paths outside the expected dictionary folder
- Monitor for outbound HTTP or SMB traffic initiated by the w3wp.exe process following spell check requests
How to Mitigate CVE-2026-13189
Immediate Actions Required
- Upgrade Progress Telerik UI for AJAX to version 2026.2.708 or later on all affected applications
- Inventory web applications for embedded Telerik components and confirm the version bundled with each deployment
- Restrict access to the spell check handler endpoint from untrusted networks until patching is complete
Patch Information
Progress has addressed CVE-2026-13189 in Telerik UI for AJAX release 2026.2.708. Application owners must update the Telerik assemblies referenced by their ASP.NET projects and redeploy. Consult the Telerik Security Advisory CVE-2026-13189 for upgrade guidance and version-specific notes.
Workarounds
- Disable the Telerik spell check handler in web.config if the feature is not required by the application
- Configure a WAF rule to reject requests to the spell check handler containing traversal sequences or absolute paths in the language parameter
- Restrict the file system permissions of the ASP.NET worker process to the minimum directories needed for application operation
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
