CriticalCVE-2021-42237

    Sitecore XP Remote Command Execution Vulnerability (CVE-2021-42237)

    Published Last modified In CISA KEV since Sources: CVE.org

    What is affected, what to do

    The vulnerability CVE-2021-42237 allows for remote code execution (RCE) via insecure deserialization in Sitecore XP versions 7.5 to 8.2 Update-7. An attacker can execute arbitrary code on the affected system without authentication or special configuration. This vulnerability is actively exploited in ransomware campaigns. Organizations should urgently update to the latest version to mitigate the risk.

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. The available sources name no fixed version. Check the vendor guidance in the references below. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Sitecore Experience Platform eq 7.5..7.5
    • Sitecore Experience Platform eq 8.0..8.0
    • Sitecore Experience Platform eq 8.1..8.1
    • Sitecore Experience Platform eq 8.2..8.2

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    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

    97.6 %

    EPSS score

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

    Source: FIRST EPSS, percentile 99.90

    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
    253.84 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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    97.6 %
    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
    99.90
    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 3 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-502

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This flaw can be exploited over the network with no authentication, no user interaction and low complexity, and it yields direct code execution as the IIS worker process. Since a public proof of concept appeared, it has ranked among the CVEs most likely to be exploited. CISA flags it for known ransomware use. Typical targets are public corporate and marketing sites, often run by agencies and left running as unattended legacy. Treat every internet-facing instance in the affected version range as critical, act immediately, and assume it is compromised until you can show otherwise. Fix instances reachable only internally within days.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Build an inventory: Find every Sitecore XP instance (CM, CD, staging, forgotten test and campaign microsites) running 7.5 Initial Release through 8.2 Update-7. Check /sitecore/shell/sitecore.version.xml or the admin login banner, and include instances hosted by agencies on your behalf.
      • Remove the vulnerable handler: Delete or rename /sitecore/shell/ClientBin/Reporting/Report.ashx on all affected instances now, as the vendor recommends. Add the removal to your deployment pipeline so it isn't redeployed. Recycle the IIS app pool and confirm the endpoint returns 404.
      • Permanent fix: Schedule an upgrade to a non-affected Sitecore XP release. A patch is available from the vendor — check the Sitecore advisory for the exact version. The 7.x/8.x line is legacy and should be migrated to a supported release anyway.
      • Check for compromise first: If the instance was internet-facing, assume it may already be compromised. Sweep the webroot for unknown .aspx, .ashx and .asmx files and new DLLs in \bin, and run a retro-hunt over IIS logs (see Detection). Trigger your IR process on any hit.
      • Rotate secrets if compromise can't be ruled out: connection strings in ConnectionStrings.config (SQL, MongoDB/xDB), Sitecore admin accounts, the machine key, and the app pool service account passwords.
      • Check reporting duties: For NIS2 entities, prepare the 24 h early warning to the national CSIRT/authority if exploitation is confirmed.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Never expose /sitecore/shell/* or /sitecore/admin/* on content delivery servers. Restrict CM servers to the editorial network or to VPN users on an IP allowlist.
      • WAF / reverse proxy: Block requests to Report.ashx case-insensitively, including URL-encoded and path-mangled variants (//, ;, %2e). Also drop POST bodies containing deserialisation gadget markers such as NetDataContractSerializer, ObjectDataProvider, System.Diagnostics.Process or TypeConfuseDelegate.
      • IPS: Enable Suricata/Snort signatures for HTTP POST to /sitecore/shell/ClientBin/Reporting/Report.ashx, such as the ET rules covering CVE-2021-42237, and run them inline in blocking mode.
      • Endpoint hardening: Use an EDR or ASR rule to stop w3wp.exe spawning cmd.exe, powershell.exe, rundll32.exe or certutil.exe. Remove the app pool identity's write access to the webroot, except for the folders it needs (App_Data, temp, upload).
      • Least privilege: Run the app pool under a dedicated, unprivileged identity. Limit the Sitecore SQL logins to the databases they need — no sysadmin, no xp_cmdshell.
      • Egress filtering: Allow outbound traffic from web servers only to required destinations. This hampers reverse shells, payload staging and C2.

    3. Runbook step 3

      Detection rules

      • IIS access logs: POSTs to Report.ashx are practically never legitimate. SPL: index=iis cs_method=POST cs_uri_stem="*/ClientBin/Reporting/Report.ashx*" | stats count by c_ip, sc_status, cs_user_agent. Pay attention to 200 or 500 responses with large request bodies.
      • Process ancestry (Sysmon EID 1 / Security 4688): Look for w3wp.exe spawning shells or recon tools. KQL: DeviceProcessEvents | where InitiatingProcessFileName =~ "w3wp.exe" and FileName in~ ("cmd.exe","powershell.exe","whoami.exe","certutil.exe","rundll32.exe").
      • Webshell drops (Sysmon EID 11): Look for w3wp.exe writing .aspx, .ashx, .asmx or .dll files under the Sitecore webroot. Sigma shape: Image|endswith: '\w3wp.exe' AND TargetFilename|endswith: ['.aspx','.ashx','.asmx'].
      • Network (Zeek/Suricata): Flag new outbound connections from Sitecore hosts to unfamiliar external IPs shortly after a Report.ashx POST. Also flag DNS lookups to out-of-band services (*.oast.*, *.burpcollaborator.net, *.interact.sh), which are typical of scanning and exploit verification.
      • Follow-on activity: Hunt for LSASS dumping, new local accounts (EID 4720) and scheduled task creation (EID 4698) on web servers. These are consistent with ransomware staging.

    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

    Sitecore XP 7.5 Initial Release to Sitecore XP 8.2 Update-7 is vulnerable to an insecure deserialization attack where it is possible to achieve remote command execution on the machine. No authentication or special configuration is required to exploit this vulnerability.

    Source: CISA KEV Catalog, NVD (NIST), cvelistv5, 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
    sitecoreexperience_platform
    • 7.5
    • 8.0
    • 8.2
    • 8.1
    • —
    • —
    • —
    • —

    Vendors and products

    Weakness classes (CWE)

    • CWE-502Deserialization of Untrusted Data

      Base

      The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.

      Entry at MITRE CWE-502

    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
    Packet StormSitecore Experience Platform XP Remote Code Execution (opens in a new tab)packetstormsecurity.comPoC (publicly reported)reported, not verified—

    References & sources

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. NVD analysis modifiedNVD

    2. Record modifiedMITRE

      2 individual changes: Reference, Reference type

      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceremoved
      http://sitecore.com
      —
      Reference typeremoved
      http://sitecore.com Types: Vendor Advisory
      —

      Source identifier: cve@mitre.org

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