Sitecore CMS Anti-CSRF Module Deserialization Remote Code Execution (RCE) Vulnerability (CVE-2019-9875)
Executive & SecOps Summary
SECOPS ASSESSMENTSitecore CMS through version 9.1
An authenticated attacker can execute arbitrary code on the target server by sending a serialized .NET object in an HTTP POST parameter.
Apply the official security patches from Sitecore or disable/update the vulnerable anti-CSRF module configuration.
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Download and apply the official security update from the Sitecore Developer Portal. After applying the patch, restart the IIS service to enforce the changes.
# Restart IIS to apply the security patch
iisreset /noforce2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, restrict access to the affected endpoints or configure Web Application Firewall (WAF) rules to block suspicious serialized payloads. Ensure the machineKey configuration is secured in web.config.
<!-- Hardening machineKey configuration in web.config -->
<configuration>
<system.web>
<machineKey validationKey='AutoGenerate,IsolateApps' decryptionKey='AutoGenerate,IsolateApps' validation='SHA1' decryption='AES' />
</system.web>
</configuration>3. Log Audit & IoC Verification Commands
Inspect IIS access logs for unusually large POST requests or parameters containing Base64-encoded .NET serialization headers (e.g., starting with AAEAAAD).
# Search IIS logs for potential .NET serialization payload signatures
grep -rn 'AAEAAAD' /var/log/iis/W3SVC1/*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 arises from the Deserialization of Untrusted Data (CWE-502) within the anti-CSRF (Cross-Site Request Forgery) protection module of Sitecore CMS. When processing incoming HTTP POST requests, the application deserializes user-supplied .NET objects without proper validation, allowing arbitrary object instantiation and execution.
2. Exploitation Mechanics & Attack Scenario
An authenticated attacker can craft a malicious serialized .NET payload using tools like ysoserial.net. By embedding this payload into an HTTP POST parameter associated with the anti-CSRF module, the attacker forces the server-side application to deserialize the untrusted object, triggering immediate remote code execution under the context of the IIS application pool identity.
3. Infrastructure & Business Impact
With a CVSS score of 8.8 and inclusion in the CISA KEV catalog, this vulnerability poses a severe threat. Successful exploitation grants the attacker full control over the web server, enabling database exfiltration, web shell deployment, and lateral movement across the internal corporate network.
Official Vendor Advisories & References
Deserialization of Untrusted Data in the anti CSRF module in Sitecore through 9.1 allows an authenticated attacker to execute arbitrary code by sending a serialized .NET object in an HTTP POST parameter.
Frequently Asked SecOps Questions (CVE-2019-9875)
FAQQ1. How critical is CVE-2019-9875 and is it actively exploited in the wild?
CVE-2019-9875 is rated CVSS 8.8 (HIGH) with a 30-day EPSS exploitation probability of 25.4%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2019-9875?
Primary impacted vendors include sitecore across sitecore_cms. Scope summary: Sitecore CMS versions up to and including 9.1
Q3. What temporary mitigations or workarounds exist for CVE-2019-9875 before patching?
[Mitigation] Apply the official security patches from Sitecore or disable/update the vulnerable anti-CSRF module configuration. Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
Generate an Internal Engineering Notice or CISO Report for CVE-2019-9875
Instantly format this advisory into an executive CISO summary or engineering patch ticket.
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