CriticalCVE-2019-9874

    Sitecore CMS and Experience Platform (XP) Deserialization Vulnerability (CVE-2019-9874)

    Published In CISA KEV since Sources: pwn.watch, CVE.org

    What is affected, what to do

    This vulnerability allows for remote code execution (RCE) in Sitecore CMS and Experience Platform (XP) via deserialization of untrusted data in the Sitecore.Security.AntiCSRF module. An unauthenticated attacker can execute arbitrary code by sending a serialized .NET object in the HTTP POST parameter __CSRFTOKEN. Affected products include Sitecore CMS versions 7.0 to 7.2 and Sitecore XP versions 7.5 to 8.2. The vulnerability is actively exploited in the wild, necessitating an urgent response. Users should promptly apply the latest security updates from Sitecore to mitigate the risk.

    The vulnerability is being actively exploited; treat it as a priority. 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 CMS and Experience Platform (XP) lte 7.0..7.2
    • Sitecore Experience Platform lte 7.5..8.2

    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: pwn.watch, CVE.org

    83.7 %

    EPSS score

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

    Source: FIRST EPSS, percentile 99.69

    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
    228.50 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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    83.7 %
    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.

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    99.69
    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 26 March 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 is network-reachable without authentication and gives code execution in the IIS worker context. With publicly available .NET deserialization gadget generators, a single crafted POST request is enough. Exploitation likelihood is very high, placing it among the CVEs most likely to be exploited, although CISA does not flag known ransomware use. Typical targets are internet-facing corporate and public-sector websites still running legacy Sitecore lines that often have not been updated for years. Treat any externally reachable 7.0–8.2 instance as critical and patch or isolate it today. Internal-only instances are high priority but can follow.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory: Identify every Sitecore instance, including CM, CD and staging servers. Affected versions are Sitecore CMS 7.0 through 7.2 and Sitecore XP 7.5 through 8.2. Check \Website\sitecore\shell\sitecore.version.xml or the assembly version of Sitecore.Kernel.dll. Also confirm whether Sitecore.Security.AntiCsrf.dll is present in bin.
      • Patch: Apply the vendor fix or upgrade for the Sitecore.Security.AntiCSRF module. The patch is available from the vendor — look up the exact version in the Sitecore security bulletin for CVE-2019-9874. These release lines are old, so verify their support status and schedule an upgrade to a supported Sitecore version.
      • Reduce exposure: If you cannot patch immediately, remove internet access to CM instances and to /sitecore/* paths, especially /sitecore/shell/ and /sitecore/admin/. Restrict access to VPN or admin networks only.
      • Emergency WAF rule: Block HTTP POST requests where the __CSRFTOKEN parameter carries a serialized .NET object stream. The typical marker is the BinaryFormatter base64 prefix AAEAAAD/////.
      • Compromise check: Sweep web roots for newly created .aspx, .ashx and .asmx files and for web shells. If you find indicators, isolate the server and preserve evidence, including a memory dump of w3wp.exe. Then rotate the secrets in ConnectionStrings.config and web.config: SQL, MongoDB and Solr credentials and the machineKey.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Separate CD and CM roles, and keep CM out of the DMZ. Enforce default-deny egress from IIS workers so that reverse shells and second-stage downloads fail.
      • WAF/IPS: Inspect the POST body. Alert on and block any __CSRFTOKEN value longer than 500 characters or containing AAEAAAD///// or /wEy (LosFormatter). Suricata shape: http.request_body; content:"__CSRFTOKEN="; content:"AAEAAAD"; distance:0; scoped to the Sitecore hosts.
      • Configuration change: Where patching is blocked, confirm with the vendor whether the AntiCSRF module can be temporarily disabled. It is wired in through App_Config\Include\Sitecore.AntiCsrf.config or the HttpModule entry in web.config. If you disable it, offset the residual CSRF risk on the admin UI with IP allow-listing.
      • Endpoint hardening: Use EDR or ASR rules to prevent w3wp.exe from spawning cmd.exe, powershell.exe, rundll32.exe or certutil.exe. Enforce AppLocker or WDAC on the web tier.
      • Least privilege: Run the application pool under a dedicated non-admin identity. Minimise write permissions on the web root and reduce the SQL rights of the Sitecore database accounts.

    3. Runbook step 3

      Detection rules

      • Process ancestry (Sysmon EID 1 / Windows EID 4688): Watch for w3wp.exe spawning shells or LOLBins. KQL: DeviceProcessEvents | where InitiatingProcessFileName =~ "w3wp.exe" and FileName in~ ("cmd.exe","powershell.exe","certutil.exe","rundll32.exe","whoami.exe")
      • File creation (Sysmon EID 11): Look for new .aspx, .ashx or .dll files under \Website\ or \inetpub\ written by w3wp.exe. Sigma shape: TargetFilename|endswith: ['.aspx','.ashx'] AND Image|endswith: '\w3wp.exe'.
      • Web logs (IIS/WAF): Look for bursts of external POST requests to Sitecore pages that return HTTP 500, which indicates failed deserialization attempts. IIS logs omit POST bodies, so also search WAF or reverse-proxy body logs for __CSRFTOKEN values with base64 serialization markers.
      • Application logs: Search the Sitecore logs (\Data\logs\log.*.txt) and the Windows Application log for exceptions from Sitecore.Security.AntiCsrf or System.Runtime.Serialization, and for SerializationException or InvalidCastException.
      • Network telemetry (Zeek/Suricata): Flag new outbound connections from the web server to unfamiliar destinations, especially on unusual ports or with DNS anomalies, shortly after a suspicious POST.

    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

    Deserialization of Untrusted Data in the Sitecore.Security.AntiCSRF (aka anti CSRF) module in Sitecore CMS 7.0 to 7.2 and Sitecore XP 7.5 to 8.2 allows an unauthenticated attacker to execute arbitrary code by sending a serialized .NET object in the HTTP POST parameter __CSRFTOKEN.

    Source: pwn.watch, 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
    sitecorecms
    • 7.0 – ≤ 7.2
    • —
    sitecoreexperience_platform
    • 7.5 – ≤ 8.2
    • —

    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

    References & sources

    • dev.sitecore.netDownloads.aspxx_refsource_MISC, Product, Vendor advisory
    • synacktiv.comblog.htmlx_refsource_MISC, Third-party advisory
    • synacktiv.comressources/advisories/Sitecore_CSRF_deserialize_RCE.pdfx_refsource_MISC, Exploit, Patch, Third-party advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2019-9874government-resource, US government resource
    • pwn.watchpwn.watch: Sitecore CMS and Experience Platform (XP): 2 exploited vulnerabilities (CVE-2019-9874, CVE-2019-9875)pwn-watch
    • support.sitecore.comSitecore advisory: Sitecore CMS and Experience Platform (XP)pwn-watch
    • support.sitecore.comSitecore advisory: Sitecore CMS and Experience Platform (XP)pwn-watch
    • NVD (NIST)NVD: CVE-2019-9874pwn-watch
    • NVD (NIST)NVD: CVE-2019-9875pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch
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