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Actively exploitedKnown ransomware use

CVE-2019-18935 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.

From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.

Our Assessment

Should You Worry?

Patch nowCybergen assessment
  • CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 3 Nov 2021.
  • CISA lists it as known to be used in ransomware campaigns.
  • Rated Critical severity (CVSS 9.8, scored by CISA).
  • It has been in the catalogue for 1,829 days. Systems still unpatched now have almost certainly been scanned for it.
The Vulnerability

What It Is

Progress Telerik UI for ASP.NET AJAX through 2019.3.1023 contains a .NET deserialization vulnerability in the RadAsyncUpload function. This is exploitable when the encryption keys are known due to the presence of CVE-2017-11317 or CVE-2017-11357, or other means. Exploitation can result in remote code execution. (As of 2020.1.114, a default setting prevents the exploit. In 2019.3.1023, but not earlier versions, a non-default setting can prevent exploitation.)

From Watch to Action

What To Do Now

  1. 1

    Find it

    Search your asset inventory and external attack surface for Progress Telerik UI for ASP.NET AJAX. Include cloud images, appliances and anything a supplier runs for you.

    Attack Surface Management
  2. 2

    Fix it

    Apply updates per vendor instructions.

    Vulnerability Management
  3. 3

    Hunt for compromise

    If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.

    Incident Response
  4. 4

    Prove it is fixed

    Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.

    Penetration Testing

Vendor Advisories

Regulation

The Compliance Clock

Cyber EssentialsRated critical, so if it affects devices in your Cyber Essentials scope, the update must be installed within 14 days of the vendor releasing it.NIS2If exploitation causes a significant incident, essential and important entities owe their CSIRT an early warning within 24 hours and a notification within 72 hours.DORAFinancial entities must classify ICT incidents and send an initial notification for a major incident within strict deadlines, with exploited flaws a common cause.US federal (BOD 22-01)Federal civilian agencies had until 3 May 2022 to remediate. A sensible benchmark for everyone else.

General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.

Stay Ahead

More Exploited Progress Flaws

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CVE-2026-8037Progress LoadMaster Command Injection VulnerabilityAdded 7 Aug 2026CVE-2024-4885Progress WhatsUp Gold Path Traversal VulnerabilityAdded 3 Mar 2025CVE-2024-1212Progress Kemp LoadMaster OS Command Injection VulnerabilityAdded 18 Nov 2024CVE-2024-6670 · RansomwareProgress WhatsUp Gold SQL Injection VulnerabilityAdded 16 Sep 2024CVE-2024-4358Progress Telerik Report Server Authentication Bypass by Spoofing VulnerabilityAdded 13 Jun 2024CVE-2023-40044 · RansomwareProgress WS_FTP Server Deserialization of Untrusted Data VulnerabilityAdded 5 Oct 2023

All 9 exploited Progress vulnerabilities

Not Sure If You Are Exposed?

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Evidence

Sources

  1. CISA Known Exploited Vulnerabilities catalogue
  2. NVD: CVE-2019-18935
  3. CVE record: CVE-2019-18935
  4. FIRST EPSS
  5. telerik.com/support/whats-new/release-history
  6. codewhitesec.blogspot.com/2019/02/telerik-revisited.html
  7. telerik.com/support/kb/aspnet-ajax/details/allows-javascriptserializer-deserialization
  8. github.com/bao7uo/RAU_crypto
  9. know.bishopfox.com/research/cve-2019-18935-remote-code-execution-in-telerik-ui
  10. github.com/noperator/CVE-2019-18935
  11. packetstormsecurity.com/files/155720/Telerik-UI-Remote-Code-Execution.html
  12. telerik.com/support/whats-new/aspnet-ajax/release-history/ui-for-asp-net-ajax-r1-2020-%28version-202