CriticalCVE-2017-9248

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

    Published In CISA KEV since Sources: CVE.org

    What is affected, what to do

    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.

    The vulnerability is being actively exploited; treat it as a priority. Update Progress Software Sitefinity to version 10.0.6412.0. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Progress Software Sitefinity lt *..10.0.6412.0
    • Progress Telerik UI for ASP.NET AJAX lte *..2017.2.503
    Fixed in
    • Progress Software Sitefinity 10.0.6412.0

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    9.8

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    9.8

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: CVE.org

    75.1 %

    EPSS score

    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.

    Source: FIRST EPSS, percentile 99.51

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    228.22 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploited
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    9.8 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    9.8
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

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    75.1 %
    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    99.51
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    CISA assessment (SSVC)
    Exploitation: active · automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 7 February 2025
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-522

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This CVE sits on KEV because it is network-reachable without authentication, trivial to exploit, and acts as the entry point for the CVE-2019-18935 RCE chain — a path that has been continuously abused by both opportunistic and targeted attackers since 2019. Exploitation likelihood is among the highest in the entire KEV catalogue, with public PoCs and automated scanners available for years. Typical targets are internet-facing ASP.NET portals, Sitefinity CMS instances and older line-of-business apps that embed Telerik components; NIS2-scope operators running legacy web apps should treat this as P1 regardless of their internal risk score and actively hunt for exposure via external attack-surface scanning (look for the Telerik.Web.UI.WebResource.axd fingerprint).

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory every IIS/ASP.NET application that ships Telerik.Web.UI.dll, including Sitefinity installs and bundled third-party web apps. Example PowerShell: Get-ChildItem -Path C:\inetpub,C:\Program Files -Recurse -Filter Telerik.Web.UI.dll | Select FullName, VersionInfo.
      • Apply the vendor patch: Telerik UI for ASP.NET AJAX R2 2017 SP1 (2017.2.621) or later, Sitefinity 10.0.6412.0 or later. Treat production systems as a change-freeze exception — CVE-2017-9248 is the prerequisite for the CVE-2019-18935 RCE chain and has been actively exploited for years.
      • If patching has to wait: generate a new, cryptographically random Telerik.Web.UI.DialogParametersEncryptionKey (minimum 128 chars) in web.config and rotate the ASP.NET <machineKey>. Both keys must be rotated again after patching because the old values are considered compromised.
      • Temporarily block the RadAsyncUpload and RadEditor dialog endpoints (Telerik.Web.UI.DialogHandler.aspx, Telerik.Web.UI.SpellCheckHandler.aspx, Telerik.Web.UI.WebResource.axd?type=rau) at the reverse proxy or WAF if the business does not need them.
      • Scan the webserver filesystem for recently created .aspx, .ashx or .dll files in upload and temp directories over the last 90 days — standard persistence after successful exploitation.

    2. Runbook step 2

      Mitigation layers

      • WAF rule: block requests to DialogHandler.aspx with a dp= parameter that is unusually long (>1500 bytes) or high-entropy; filter outbound Base64 payloads containing JSON fragments such as "EnableAsyncUpload":true.
      • Network segmentation: force the web tier through defined egress proxies; outbound traffic from w3wp.exe to external IPs is a strong compromise indicator and should be logged at the perimeter.
      • Least privilege for IIS AppPool identities: no write permissions for IIS_IUSRS on the web root; restrict upload directories via <handlers> to static content only (<add name="StaticFile" .../>).
      • Filesystem hardening: remove Execute permission from all upload directories in IIS (handlers accessPolicy="Read") so dropped webshells cannot run.
      • Set <machineKey> with AutoGenerate=false and explicit, per-environment keys; rotate across web farms after any known incident. Never store keys in source repos or deployment templates in cleartext.
      • For legacy Telerik installs that cannot be patched, front them with an authenticated reverse proxy (e.g. Entra Application Proxy with MFA) or decommission them entirely.

    3. Runbook step 3

      Detection rules

      • IIS access logs: GET/POST against Telerik.Web.UI.DialogHandler.aspx or Telerik.Web.UI.SpellCheckHandler.aspx with abnormally long query strings. KQL: W3CIISLog | where csUriStem endswith "DialogHandler.aspx" | where strlen(csUriQuery) > 1000 or scStatus in (500,302).
      • Sysmon EID 1 (Process Create): w3wp.exe as parent of cmd.exe, powershell.exe, csc.exe or rundll32.exe — almost always a webshell indicator. Sigma shape: parent_image|endswith: '\w3wp.exe' + image|endswith: '\powershell.exe'.
      • Sysmon EID 11 (File Create): new .aspx, .asmx or .ashx files under the app path written by w3wp.exe, especially in Telerik.Web.UI.DialogHandler temp paths or App_Data.
      • Network telemetry (Zeek/Suricata): repeated requests from the same client IP to DialogHandler.aspx with steadily changing dp= parameters within a short window — classic brute-force pattern against the DialogParametersEncryptionKey.
      • Windows Event ID 4663 / auditd: write access by the IIS AppPool account to directories outside the expected content path, especially C:\Windows\Temp and the AppPool user's %TEMP%.

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    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.

    Source: NVD (NIST), cvelistv5, CISA KEV Catalog, CVE.org (MITRE)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    progresssitefinity
    • < 10.0.6412.0
    • 10.0.6412.0
    telerikui_for_asp.net_ajax
    • ≤ 2017.2.503
    • —

    Vendors and products

    Weakness classes (CWE)

    • CWE-522Insufficiently Protected Credentials

      Class

      The product transmits or stores authentication credentials, but it uses an insecure method that is susceptible to unauthorized interception and/or retrieval.

      Entry at MITRE CWE-522

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited
    Exploit-DBEDB-ID 43873 (opens in a new tab)exploit-db.comPoC (publicly reported)reported, not verified—

    References & sources

    • telerik.comsupport/kb/aspnet-ajax/details/cryptographic-weaknessx_refsource_CONFIRM, Mitigation, Vendor advisory
    • exploit-db.com43873Exploit, x_refsource_EXPLOIT-DB, Exploit, Third-party advisory, Vulnerability database
    • telerik.comblogs/security-alert-for-telerik-ui-for-asp.net-ajax-and-progre…x_refsource_CONFIRM, Vendor advisory
    • securityfocus.com99965Vulnerability database, x_refsource_BID, Broken link, Third-party advisory, Vulnerability database
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2017-9248government-resource, US government resource
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