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Actively exploited

CVE-2017-9248 Progress Telerik UI for ASP.NET AJAX and Sitefinity Cryptographic Weakness Vulnerability

Progress Telerik UI for ASP.NET AJAX and Sitefinity have a cryptographic weakness in Telerik.Web.UI.dll that can be exploited to disclose encryption keys (Telerik.Web.UI.DialogParametersEncryptionKey and/or the MachineKey), perform cross-site-scripting (XSS) attacks, compromise the ASP.NET ViewState, and/or upload and download files.

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.
  • 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

Telerik.Web.UI.dll in Progress Telerik UI for ASP.NET AJAX before R2 2017 SP1 and Sitefinity before 10.0.6412.0 does not properly protect Telerik.Web.UI.DialogParametersEncryptionKey or the MachineKey, which makes it easier for remote attackers to defeat cryptographic protection mechanisms, leading to a MachineKey leak, arbitrary file uploads or downloads, XSS, or ASP.NET ViewState compromise.

From Watch to Action

What To Do Now

  1. 1

    Find it

    Search your asset inventory and external attack surface for Progress ASP.NET AJAX and Sitefinity. 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?

Our attack surface and vulnerability teams can check your internet-facing estate for CVE-2017-9248 and every other exploited flaw on the list.

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Evidence

Sources

  1. CISA Known Exploited Vulnerabilities catalogue
  2. NVD: CVE-2017-9248
  3. CVE record: CVE-2017-9248
  4. FIRST EPSS
  5. telerik.com/support/kb/aspnet-ajax/details/cryptographic-weakness
  6. exploit-db.com/exploits/43873/
  7. telerik.com/blogs/security-alert-for-telerik-ui-for-asp.net-ajax-and-progress-sitefinity
  8. securityfocus.com/bid/99965