CVE-2021-42237: Sitecore XP insecure deserialization enables unauthenticated remote code execution

Automated analysis

Generated by VULONE's analysis model from the NVD record, CISA KEV and EPSS data on 16 September 2026. Confidence: high.

critical priorityUnauthenticated network-reachable RCE with a 9.8 CVSS score, KEV listing, ransomware use and near-maximum EPSS probability.

What it is

Sitecore XP 7.5 Initial Release through 8.2 Update-7 deserializes untrusted data, allowing an attacker to run arbitrary commands on the host. No authentication or special configuration is needed, so any reachable instance is exposed. The flaw is tracked in CISA KEV with known ransomware use, making it a high-value target for both initial access and destructive campaigns.

Impact

An attacker gains remote command execution on the Sitecore server, which typically means full control of the web application, its data and the underlying host. From there they can pivot into internal networks, steal credentials or deploy ransomware.

Attack surface

Reachable over the network via the Sitecore XP web interface; the CVSS vector shows AV:N/PR:N/UI:N, so no credentials and no user interaction are required. Any internet- or intranet-exposed instance in the affected version range is a candidate.

Exploitation

Listed in CISA KEV since 2022-03-25 with known ransomware campaign use, and EPSS 30-day probability is 0.979 (99.9th percentile). Public exploit references exist, so exploitation is active and widespread.

What to do

• Apply the vendor update per Sitecore KB1000776; upgrade off the affected 7.5 to 8.2 Update-7 range.
• If patching cannot be done immediately, remove or restrict network access to the Sitecore XP instance, especially from the internet.
• Place the instance behind a WAF or reverse proxy with rules targeting deserialization payloads, understanding this is only a stopgap.
• Rotate credentials and secrets stored on or reachable from the Sitecore host, and review for signs of prior compromise.
• Monitor CISA KEV guidance and confirm the due date of 2022-04-15 has been met for your environment.

Detection

• Hunt web server and Sitecore logs for POST requests to Sitecore endpoints containing serialized .NET payload markers or unusually large binary bodies.
• Alert on child processes spawned by the Sitecore/IIS worker process (w3wp.exe), such as cmd.exe, powershell.exe or net.exe.
• Monitor for outbound connections from the Sitecore host to unfamiliar IPs, consistent with post-exploitation or ransomware staging.
• Review file system and registry changes on the Sitecore server for webshells or new scheduled tasks.

This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.