CVE-2026-13183 Overview
CVE-2026-13183 affects Progress Telerik UI for AJAX versions prior to v2026.2.708. The RadAsyncUpload component processes upload metadata in a way that leaks cryptographic validity through measurable timing differences. Remote attackers can exploit this side channel to recover protected metadata values without authentication.
The vulnerability is categorized under [CWE-208] Observable Timing Discrepancy. It is exploitable over the network with low attack complexity and no user interaction. Successful exploitation compromises the confidentiality of protected upload metadata handled by the component.
Critical Impact
Remote unauthenticated attackers can recover cryptographically protected RadAsyncUpload metadata by measuring server response timing, undermining the integrity guarantees of the upload handler.
Affected Products
- Progress Telerik UI for AJAX prior to v2026.2.708
- Applications embedding the RadAsyncUpload control
- ASP.NET AJAX web applications built on affected Telerik releases
Discovery Timeline
- 2026-07-22 - CVE-2026-13183 published to NVD
- 2026-07-22 - Last updated in NVD database
Technical Details for CVE-2026-13183
Vulnerability Analysis
The RadAsyncUpload control accepts client-submitted metadata that is cryptographically protected to prevent tampering. When the server processes this metadata, validation routines take measurably different amounts of time depending on how far validation proceeds before failing. An attacker who submits crafted metadata and measures response latency can distinguish valid from invalid states one byte at a time.
This pattern is a classic timing oracle. By iterating through candidate values and correlating server response times, an attacker reconstructs the protected metadata content. The vulnerability does not require authentication because the upload endpoint is exposed to any network-reachable client.
Root Cause
The underlying flaw is a non-constant-time comparison or validation path in the metadata processing routine. Cryptographic checks must complete in identical time regardless of input to prevent side-channel leakage. Telerik addressed the issue in v2026.2.708 by hardening the validation logic against timing observation.
Attack Vector
An unauthenticated remote attacker sends repeated HTTP requests to the RadAsyncUpload handler with crafted metadata payloads. The attacker measures response times with statistical precision to identify byte-level correctness. Over many requests, the attacker recovers the protected values used by the upload subsystem. No user interaction is required and the attack proceeds entirely over the network.
The vulnerability is described in prose because no public proof-of-concept code is available. See the Telerik Security Advisory CVE-2026-13183 for vendor technical details.
Detection Methods for CVE-2026-13183
Indicators of Compromise
- High volumes of requests to Telerik.Web.UI.WebResource.axd or RadAsyncUpload endpoints from a single source over a short window
- Repeated upload requests containing near-identical metadata blobs with small byte variations
- Anomalous HTTP request patterns targeting file upload endpoints without completing legitimate uploads
Detection Strategies
- Monitor web server and WAF logs for burst request patterns against RadAsyncUpload handlers indicative of timing measurement
- Alert on statistically abnormal request rates to file upload endpoints from non-interactive clients
- Correlate elevated request volumes with variance in request payload structure to identify oracle probing
Monitoring Recommendations
- Enable verbose logging on Telerik upload endpoints and forward logs to a centralized SIEM for correlation
- Track per-source request latencies and rates against RadAsyncUpload to baseline normal traffic
- Review authentication and session context for all requests reaching the upload handler
How to Mitigate CVE-2026-13183
Immediate Actions Required
- Upgrade Progress Telerik UI for AJAX to v2026.2.708 or later across all applications
- Inventory all deployed applications that reference Telerik.Web.UI assemblies and confirm patched versions are loaded
- Restrict network exposure of RadAsyncUpload endpoints to trusted clients where feasible
Patch Information
Progress released the fix in Telerik UI for AJAX v2026.2.708. The update introduces constant-time processing for RadAsyncUpload metadata validation, eliminating the timing side channel. Refer to the Telerik Security Advisory CVE-2026-13183 for upgrade instructions and version guidance.
Workarounds
- Deploy a web application firewall rule to rate-limit requests to RadAsyncUpload endpoints per source IP
- Restrict access to upload endpoints behind authentication or network access controls until patching is complete
- Disable the RadAsyncUpload control in applications that do not require asynchronous upload functionality
# Example WAF rate-limit configuration (ModSecurity)
SecRule REQUEST_URI "@contains Telerik.Web.UI.WebResource.axd" \
"id:1013183,phase:1,pass,nolog,\
setvar:ip.rau_count=+1,expirevar:ip.rau_count=60"
SecRule IP:RAU_COUNT "@gt 30" \
"id:1013184,phase:1,deny,status:429,\
msg:'Rate limit exceeded on RadAsyncUpload endpoint'"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
