Telerik RadAsyncUpload Timing Side-Channel Metadata Leak

CVE-2026-13183 affects Progress Telerik UI for AJAX versions prior to v2026.2.708 and represents a timing side-channel vulnerability in the RadAsyncUpload component's metadata processing. Attackers can exploit measurable timing differences in cryptographic validity checks to recover protected metadata values without direct access to encryption keys. This vulnerability matters because it undermines the security of file upload workflows—a critical component in many enterprise web applications. Organizations using affected Telerik UI versions for AJAX, particularly those handling sensitive file uploads in healthcare, finance, or government sectors, face risk of metadata exposure that could reveal system architecture, user patterns, or confidential information embedded in upload parameters.

While this CVE does not map directly to MITRE ATT&CK techniques, Casky's Claude-powered analysis would detect the attack patterns associated with timing-based cryptanalysis and reconnaissance activity. Practitioners using Casky would observe findings related to T1592 (Gather Victim Org Information) and T1598 (Phishing) patterns, as timing exfiltration often precedes social engineering or targeted attacks. The platform's extended reasoning capability would help security teams recognize the distinction between normal upload latency and deliberate timing measurements—flagging suspicious request patterns with consistent response-time probing, repeated upload attempts with varying payloads designed to measure processing delays, or anomalous sequences of failed validation checks that correlate with timing analysis. Teams would receive alerts on unpatched Telerik versions and recommendations to upgrade to v2026.2.708 or later immediately.