CVE-2021-42237

CVE-2021-42237 is a critical-severity vulnerability in Sitecore Experience Platform with a CVSS 3.x base score of 9.8. It is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, confirming it has been exploited in the wild (added 2022-03-25). The underlying weakness is classified as CWE-502.

Key facts

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.

CVE-2021-42237: Sitecore XP Insecure Deserialization Leading to Unauthenticated Remote Code Execution

AI-generated analysis based on the vulnerability data on this page.

Attribute Value
CVE ID CVE-2021-42237
CWE CWE-502: Deserialization of Untrusted Data
CVSS v2 10.0 (AV:N/AC:L/Au:N/C:C/I:C/A:C)
CVSS v3.1 9.8 Critical (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)
EPSS 0.99214 (99.9th percentile)
Known Exploited Yes (CISA KEV, 2022-03-25)
EU Exploited Yes (EUVD-2021-29215, since 2022-03-25)
Affected Product Sitecore Experience Platform (XP) 7.5 Initial Release – 8.2 Update-7

Summary

Sitecore XP 7.5 through 8.2 Update-7 is vulnerable to an insecure deserialization attack. A remote, unauthenticated attacker can send a crafted request containing a malicious serialized object that, when deserialized by the application, results in arbitrary command execution on the underlying host. No authentication or special configuration is required to exploit this flaw.

Background

Sitecore Experience Platform (XP) is a widely adopted enterprise content management and digital experience platform. The .NET-based product exposes various endpoints and handlers that process user-supplied data. In affected versions, certain code paths accept serialized objects without adequate validation, a classic and dangerous pattern in ASP.NET and .NET applications.

Root Cause

The vulnerability is rooted in CWE-502: Deserialization of Untrusted Data. Specifically, the application deserializes attacker-controlled input using a format (commonly BinaryFormatter or similar .NET serialization gadgets in this class of bugs) without restricting the expected types or validating the data stream. When a malicious payload is deserialized, it triggers a chain of gadget calls that eventually leads to arbitrary code execution on the server. The lack of authentication requirements means the attack surface is fully exposed to the network.

Impact

The CVSS v3.1 score of 9.8 (Critical) reflects the severity:

  • Attack Vector (AV): Network – exploitable remotely without local access.
  • Attack Complexity (AC): Low – no special conditions or race windows are needed.
  • Privileges Required (PR): None – no account or credentials are necessary.
  • User Interaction (UI): None – fully automated exploitation is possible.
  • Scope (S): Unchanged – the vulnerable component is the only component impacted.
  • Confidentiality, Integrity, Availability (C/I/A): High – complete system compromise is achievable.

Given the EPSS score of 0.99214 and inclusion in the CISA Known Exploited Vulnerabilities (KEV) catalog as of March 2022, this vulnerability carries an exceptionally high probability of active exploitation in the wild.

Exploitation Walkthrough

Ethics and Scope: The following is a defensive, high-level description of how exploitation occurs. No weaponized exploit code is provided. Security professionals may use this understanding to build detections and validate compensating controls.

Attackers typically identify an exposed Sitecore instance and locate an endpoint that accepts serialized data. A crafted payload—embedding a known .NET deserialization gadget chain—is submitted to this endpoint. When the server deserializes the payload, the gadget chain executes operating-system commands under the identity of the application pool or web service account. Because no authentication handshake is required, the entire kill chain can be completed in a single HTTP request. Defenders should assume that public exploit artifacts for this vulnerability exist and are actively used by both opportunistic and targeted threat actors.

Affected and Patched Versions

Affected:

  • Sitecore XP 7.5 Initial Release
  • Sitecore XP 7.5 Update-1
  • Sitecore XP 7.5 Update-2
  • Sitecore XP 8.0 (initial release through Update-7)
  • Sitecore XP 8.1 (initial release through Update-3)
  • Sitecore XP 8.2 (initial release through Update-7)

Patched:

  • Upgrade to a Sitecore release that includes the security fix (see Sitecore Support KB1000776 for specific patch and update guidance).

Remediation

  1. Upgrade immediately. Apply the official patch or upgrade to a non-vulnerable Sitecore version as directed in Sitecore Support KB1000776.
  2. Compensating controls: If immediate patching is not feasible, restrict network access to the Sitecore instance to authorized administrators and trusted integrations only. Deploy a Web Application Firewall (WAF) rule set that inspects for anomalous serialized payloads, recognizing that this is a temporary control and not a substitute for patching.
  3. Review application architecture. Move the Sitecore content delivery or management endpoints behind a VPN or reverse proxy that enforces strong authentication.

Detection

  • Monitor web server logs for unusually large or binary-encoded POST bodies directed at known Sitecore handlers and endpoints.
  • Look for child process spawning from the Sitecore application pool identity (e.g., cmd.exe, powershell.exe, or unexpected executables).
  • Correlate endpoint detection alerts with inbound traffic from untrusted IPs to Sitecore URLs.
  • Hunt for deserialization-related exceptions in application logs that may indicate failed exploitation attempts.

Assessment

This vulnerability is a textbook example of why untrusted deserialization remains a top-tier risk in .NET applications. The EPSS of 0.99214 and KEV listing confirm that threat actors have weaponized and deployed this flaw at scale. The combination of unauthenticated network access, low attack complexity, and complete system impact makes CVE-2021-42237 one of the most severe vulnerabilities in the Sitecore ecosystem. Two key lessons stand out: (1) Never deserialize user-controlled input without strict type constraints and integrity checks, and (2) internet-facing enterprise applications must be patched or isolated on an accelerated timeline once proof-of-concept code becomes public.

References

Frequently asked questions

What is CVE-2021-42237?
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.
How severe is CVE-2021-42237?
CVE-2021-42237 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-42237 being actively exploited?
Yes. CVE-2021-42237 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2022-03-25, which means active exploitation has been confirmed. It should be prioritised for remediation.
What products are affected by CVE-2021-42237?
CVE-2021-42237 primarily affects Sitecore Experience Platform. In total, 24 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-42237?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.
Does CVE-2021-42237 have an EU (EUVD) identifier?
Yes. CVE-2021-42237 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2021-29215. It is also flagged as exploited in the EUVD (since 2022-03-25).
When was CVE-2021-42237 published?
CVE-2021-42237 was published on 2021-11-05 and last updated on 2026-07-06.

References

Affected products (24)

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