CriticalCVE-2017-11357

    Telerik UI for ASP.NET AJAX Insecure Direct Object Reference Vulnerability (CVE-2017-11357)

    Published In CISA KEV since Sources: CVE.org

    What is affected, what to do

    Progress Telerik UI for ASP.NET AJAX before R2 2017 SP2 does not properly restrict user input to RadAsyncUpload, which allows remote attackers to perform arbitrary file uploads or execute arbitrary code.

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. Update Progress Software Telerik UI for ASP.NET AJAX to version 2020.1.114. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Progress Software Telerik UI for ASP.NET AJAX lt *..2020.1.114
    Fixed in
    • Progress Software Telerik UI for ASP.NET AJAX 2020.1.114

    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

    77.7 %

    EPSS score

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

    Source: FIRST EPSS, percentile 99.56

    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
    253.30 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.

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    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.

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    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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    77.7 %
    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
    99.56
    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

    Response and mitigation

    Why act now?

    Prioritisation rationale

    The flaw is exploitable over the network with no authentication and no user interaction. Public exploit code has circulated for years. Telerik RAU abuse is a recurring entry vector against IIS-hosted .NET applications, and CISA flags it as used in ransomware campaigns. Typical targets are internet-facing .NET web apps at public bodies, utilities and mid-market firms, often legacy or third-party applications where nobody knows Telerik is present. Exploitation likelihood is very high. Treat every externally reachable instance as critical and patch or disable it within 24 hours. Internal-only instances can follow in the current maintenance window.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory Telerik assemblies: Search all IIS servers and build artefacts for Telerik.Web.UI.dll and read the file version, e.g. Get-ChildItem -Recurse -Filter Telerik.Web.UI.dll | % { $_.VersionInfo.FileVersion }. Include third-party products (CMS, line-of-business apps, vendor portals). Telerik is frequently bundled without anyone noticing.
      • Patch: Every build before R2 2017 SP2 is vulnerable. Move to a current, supported Telerik UI for ASP.NET AJAX release; take the exact target version from the Progress vendor advisory. Version 2020.1.114 is also listed as affected in the context. Stopping at R2 2017 SP2 is not enough, because RadAsyncUpload has follow-on flaws (e.g. CVE-2019-18935).
      • Disable RadAsyncUpload if unused: Add <add key="Telerik.Web.DisableAsyncUploadHandler" value="true" /> under <appSettings> in web.config. This immediately disables the Telerik.Web.UI.WebResource.axd?type=rau handler.
      • Rotate cryptographic keys: Set unique random values for Telerik.AsyncUpload.ConfigurationEncryptionKey, Telerik.Upload.ConfigurationHashKey and Telerik.Web.UI.DialogParametersEncryptionKey. Also regenerate the ASP.NET machineKey.
      • Compromise assessment on internet-facing hosts: Check upload temp locations (App_Data\RadUploadTemp, %WINDIR%\Temp, the app pool account's %TEMP%) for unexpected .dll, .aspx or .ashx files. If you find any, isolate the host and trigger incident handling, including the NIS2 reporting assessment.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Put Telerik-based apps that don't need public exposure behind VPN or a pre-authenticating reverse proxy. Apply default-deny egress on IIS servers to break reverse shells and second-stage downloads.
      • WAF/IPS: Block or tightly inspect POST requests to Telerik.Web.UI.WebResource.axd with type=rau from untrusted sources. Also block multipart bodies containing rauPostData together with executable extensions (.dll, .aspx, .exe). Public Suricata and Snort signatures exist for Telerik RAU exploitation. Update your ruleset and switch those rules from alert to drop.
      • Endpoint hardening: Use AppLocker or WDAC to stop w3wp.exe from loading unsigned DLLs from temp and upload directories. Enable your EDR's policy blocking child processes of web server workers.
      • Least privilege: Run the IIS app pool as a dedicated ApplicationPoolIdentity without local admin rights. Restrict write access to the upload temp folder and deny execute on it via NTFS.
      • Configuration: Explicitly set AllowedFileExtensions and TemporaryFolder on RadAsyncUpload, and cap the maximum upload size.

    3. Runbook step 3

      Detection rules

      • IIS access logs: Look for POST to /Telerik.Web.UI.WebResource.axd with cs-uri-query containing type=rau from external IPs, especially with status 200 and unusual user agents. SPL: index=iis cs_method=POST cs_uri_stem="*Telerik.Web.UI.WebResource.axd" cs_uri_query="*type=rau*" | stats count by c_ip, s_ip
      • Sysmon EID 11 (FileCreate): Image ends with \w3wp.exe and TargetFilename ends with .dll, .aspx or .ashx under \Temp\ or \RadUploadTemp\.
      • Sysmon EID 7 (ImageLoad): w3wp.exe loads a DLL from C:\Windows\Temp\ or a user temp path. This is a high-fidelity indicator of RadAsyncUpload deserialisation exploitation.
      • EDR process ancestry / Sysmon EID 1 / Security EID 4688: Alert on w3wp.exe → cmd.exe/powershell.exe/rundll32.exe/certutil.exe. KQL: DeviceProcessEvents | where InitiatingProcessFileName =~ "w3wp.exe" and FileName in~ ("cmd.exe","powershell.exe","rundll32.exe","certutil.exe")
      • Network telemetry (Zeek/Suricata): Flag new outbound connections from IIS hosts to unknown external destinations within 5 minutes of a type=rau POST, correlated via conn.log.

    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

    Progress Telerik UI for ASP.NET AJAX before R2 2017 SP2 does not properly restrict user input to RadAsyncUpload, which allows remote attackers to perform arbitrary file uploads or execute arbitrary code.

    Source: CISA KEV Catalog, cvelistv5, NVD (NIST), 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
    progresstelerik_ui_for_asp.net_ajax
    • < 2020.1.114
    • 2020.1.114

    Vendors and products

    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 43874 (opens in a new tab)exploit-db.comPoC (publicly reported)reported, not verified—

    References & sources

    • exploit-db.com43874Exploit, x_refsource_EXPLOIT-DB
    • telerik.comsupport/kb/aspnet-ajax/upload-(async)/details/insecure-direct-o…x_refsource_CONFIRM
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2017-11357government-resource
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