How severe is CVE-2021-42237?

CVE-2021-42237 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which products are affected by CVE-2021-42237?

CVE-2021-42237 affects the following products: sitecore experience platform.

How do I patch CVE-2021-42237?

No patch has shipped for CVE-2021-42237 yet — track the sitecore experience platform advisory for a fixed release and apply the workarounds below in the meantime.

How do I detect CVE-2021-42237 across my infrastructure?

Inventory every sitecore experience platform deployment and check each version against the affected-products list above.

How do I mitigate CVE-2021-42237 if there is no patch (or I can't update yet)?

Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade. Alongside that, restrict the management interface to trusted networks and apply the vendor's recommended configuration mitigations.

Is CVE-2021-42237 actively exploited in the wild?

Yes. There are 8 known exploit references for CVE-2021-42237, including 7 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-42237?

CVE-2021-42237 has an EPSS (Exploit Prediction Scoring System) score of 97.6%, placing it in the 100th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. A score above 50% indicates significantly elevated exploitation risk — immediate patching is strongly recommended.

What type of vulnerability is CVE-2021-42237?

CVE-2021-42237 is classified as Deserialization of Untrusted Data (CWE-502). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

Which products and versions are affected by CVE-2021-42237?

CVE-2021-42237 affects sitecore experience platform (4 versions, e.g. 7.5, 8.0, 8.1…). Check the affected-products list on this page against your deployed version to confirm exposure.

Is there exploit tooling available for CVE-2021-42237?

A Nuclei detection template exists for CVE-2021-42237, meaning automated scanners can fingerprint it. Public exploit tooling significantly increases real-world risk — prioritize patching and ensure detection coverage. Exploit tooling should only ever be used in isolated, authorized testing environments.

When was CVE-2021-42237 published, and has it been updated?

CVE-2021-42237 was published on November 5, 2021 and was last updated on July 9, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🛡️

Not in CISA KEV

CRITICAL severity

CVE-2021-42237 — Experience Platform

CRITICAL

CVE-2021-42237 is a critical-severity (CVSS 9.8) Deserialization of Untrusted Data vulnerability in sitecore experience platform. 8 public exploit references exist, so weaponization risk is real. No vendor fix is recorded yet; mitigation options are listed below.

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.…

Published

Nov 5, 2021

Updated

Jul 9, 2026

Affected

1 product

Patched

See advisory

Exploits

8 known

Exploitation data as of Oct 24, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Actively exploited in the wild

CISA’s SSVC triage classifies this CVE as under active exploitation.
CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
A successful exploit gives an attacker total control of the affected component, not partial access.

Exploitation and automatability from CISA’s SSVC triage for CVE-2021-42237.

EPSS Exploitation Probability

via FIRST.org ↗

97.6%probability of exploitation in next 30 days

Very High Risk-0.34%

Lower risk than most CVEs100th percentile — riskier than 100% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-42237 by exploitation likelihood (EPSS) against impact (CVSS). In the shaded patch-first corner (EPSS 50%+, CVSS 7.0+).

Where this sits among everything scored

Of 395,308 CVEs with a current EPSS score, this one falls in the ≥ 90% band (highlighted). Counts from FIRST.org, log-scaled.

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.

Affected Products

1 product · 24 configurations

Application

experience platformsitecore

4 versions

7.58.08.18.2

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.