Telerik UI for ASP.NET AJAX Cryptographic Weakness Vulnerability Analysis and Mitigation Guide (CVE-2017-9248)
Executive & SecOps Summary
SECOPS ASSESSMENTProgress Telerik UI for ASP.NET AJAX versions prior to R2 2017 SP1, and Sitefinity versions prior to 10.0.6412.0
Attackers can compromise cryptographic protections to leak the MachineKey, perform arbitrary file uploads/downloads, execute XSS, or compromise ASP.NET ViewState to achieve Remote Code Execution (RCE)
Upgrade to the latest secure version or manually configure a strong, unique DialogParametersEncryptionKey and MachineKey in web.config
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Upgrade Telerik UI for ASP.NET AJAX to version R2 2017 SP1 (2017.2.621) or later. Run the following command in the NuGet Package Manager Console:
# Update Telerik UI via NuGet Package Manager
Update-Package Telerik.Web.UI -Version 2017.2.6212. Temporary Workaround & Hardening Configuration
If an immediate upgrade is not feasible, explicitly define a strong, unique 48-character hexadecimal string for Telerik.Web.UI.DialogParametersEncryptionKey in the <appSettings> section of your web.config.
<!-- web.config Hardening -->
<configuration>
<appSettings>
<!-- Set a unique, unpredictable cryptographic key -->
<add key='Telerik.Web.UI.DialogParametersEncryptionKey' value='3f2d5e6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1b2c3d4e' />
</appSettings>
</configuration>3. Log Audit & IoC Verification Commands
Inspect IIS web server logs for high-frequency requests targeting Telerik.Web.UI.DialogHandler accompanied by 500 Internal Server Errors. Use the following PowerShell script to verify the version of the deployed DLL:
# PowerShell script to check Telerik.Web.UI.dll version
$dllPath = 'C:\inetpub\wwwroot\bin\Telerik.Web.UI.dll'
if (Test-Path $dllPath) {
$versionInfo = [System.Diagnostics.FileVersionInfo]::GetVersionInfo($dllPath)
Write-Host 'Current Telerik UI Version:' $versionInfo.ProductVersion
} else {
Write-Host 'Telerik.Web.UI.dll not found.'
}Block Exploits Instantly with Managed Virtual Patching Rules
Can't patch production immediately? Deploy managed WAF rules at the edge to intercept RCE, SQLi, and deserialization payloads before they hit your origin server.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability exists in the Telerik.Web.UI.dll library due to insecure handling of the DialogParametersEncryptionKey and the ASP.NET MachineKey. Under default configurations, weaknesses in the encryption algorithm and predictable key generation mechanisms allow remote attackers to perform brute-force or padding oracle attacks on encrypted query strings to recover the encryption keys.
2. Exploitation Mechanics & Attack Scenario
An attacker sends crafted requests to the Telerik UI DialogHandler component (Telerik.Web.UI.DialogHandler.aspx). By analyzing error responses or timing differences, the attacker decrypts and leaks the encryption keys. Once the keys are obtained, the attacker can forge valid dialog parameters to access file upload handlers, upload malicious web shells, or tamper with the ASP.NET ViewState to execute arbitrary code on the server.
3. Infrastructure & Business Impact
As a high-severity vulnerability listed in the CISA KEV catalog, this flaw is actively exploited in the wild. Successful exploitation grants the attacker full control over the web server, potentially leading to lateral movement, database compromise, ransomware deployment, and severe business disruption.
Official Vendor Advisories & References
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.
Frequently Asked SecOps Questions (CVE-2017-9248)
FAQQ1. How critical is CVE-2017-9248 and is it actively exploited in the wild?
CVE-2017-9248 is rated CVSS 9.8 (CRITICAL) with a 30-day EPSS exploitation probability of 75.1%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2017-9248?
Primary impacted vendors include progress, telerik across telerik_ui_for_asp.net_ajax, sitefinity. Scope summary: Progress Telerik UI for ASP.NET AJAX before R2 2017 SP1 (2017.2.621), and Progress Sitefinity before 10.0.6412.0
Q3. What temporary mitigations or workarounds exist for CVE-2017-9248 before patching?
[Mitigation] Upgrade to the latest secure version or manually configure a strong, unique DialogParametersEncryptionKey and MachineKey in web.config Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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