IRONSMITHINTEL
CRITICALCVSS9.8
|
Actively Exploited
|CISA KEV|CVE-2019-18935|Auth: none — unauthenticated|Reboot: required|Manual only

Progress Telerik UI for ASP.NET AJAX Deserialization of Untrusted Data Vulnerability

Progress Telerik UI for ASP.NET AJAX contains a deserialization of untrusted data vulnerability through RadAsyncUpload which leads to code execution on the server in the context of the w3wp.exe process.

Published Dec 11, 2019 · Updated May 16, 2026
Why patchRisk explained in plain English
Worst-case scenarioIf unpatched

A remote attacker, without authentication, can achieve full data confidentiality loss, arbitrary modification of data, complete denial of service or system unavailability. CISA has confirmed use of this vulnerability in known ransomware campaigns — treat as high priority for remediation. Federal agencies are required to remediate by 2022-05-03 under CISA BOD 22-01.

How the attack worksNo clicks needed

This is a Deserialization of Untrusted Data (CWE-502) vulnerability in Progress Telerik UI for ASP.NET AJAX. Exploitation requires remote network access, low attack complexity, no authentication required, and no user interaction required.

📧

Phishing link

🖼

Malicious file

🔓

Server compromised

Am I affected?Quick check

Probably yes if any of these apply:

IT Security
Running ui for asp.net ajax: 2011.1.315 ≤ v ≤ 2020.1.114
Real-world incidentsWhat we've seen

Used in known ransomware campaigns. Threat-research write-up: http://packetstormsecurity.com/files/159653/Telerik-UI-ASP.NET-AJAX-RadAsyncUpload-Deserialization.html

How to patch

Manual remediation steps

Apply the Vendor Patch

This vulnerability is in the CISA Known Exploited Vulnerabilities catalog — apply the vendor's security update as soon as possible.

CISA required action: Apply updates per vendor instructions.

References

    1
    Vendor advisory: https://www.telerik.com/support/kb/aspnet-ajax/details/allows-javascriptserializer-deserialization
    1
    NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2019-18935
    1
    CISA KEV: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2019-18935
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