⚠ Reference material — not professional advice. Test in staging, back up first, verify against your specific version. Use your own judgment for your environment.
● High · CVSS 8.8 ⚠ ACTIVELY EXPLOITED — CISA KEV

How to Fix CVE-2019-9875: Insecure Deserialization in CMS and Experience Platform (XP)

By Sai Kiran Pandrala

⚡ At a glance
SeverityCVSS 8.8 - High
Actively exploited?Yes, listed in CISA KEV (added 2025-03-26)
AffectedCMS and Experience Platform (XP) (see advisory for affected versions)
Fixed inSee vendor advisory
Type (CWE)Not verified - see official advisory

Patch immediately. CISA added CVE-2019-9875 to the Known Exploited Vulnerabilities catalog on 2025-03-26. Federal civilian agencies must remediate by 2025-04-16. Treat every internet-reachable instance as a priority patch.

What is CVE-2019-9875?

CVE-2019-9875 is an Insecure Deserialization flaw in Sitecore CMS and Experience Platform (XP). It carries a CVSS base score of 8.8 (high). CISA confirmed real-world exploitation by adding it to the Known Exploited Vulnerabilities catalog on 2025-03-26.

From the source record: 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.

Why it matters in practice: KEV-listed CVEs draw continuous internet-wide scanning. Any unpatched, internet-reachable installation is on borrowed time. The blast radius depends on how the affected service is exposed. An internet-facing instance with no compensating controls is the highest-risk configuration.

Am I affected?

You are affected if your installation of CMS and Experience Platform (XP) matches a version listed in the Affected row above.

Check the installed version of CMS and Experience Platform (XP) against the Affected row above. If the version sits at or below the affected range and the vendor patch has not been applied, you are vulnerable.

How to fix CVE-2019-9875

Apply the vendor patch. Target the patched build listed on the vendor advisory. The runnable command set below covers the most common deployment patterns for CMS and Experience Platform (XP).

Generic upgrade path


# Debian / Ubuntu
sudo apt-get update && sudo apt-get install --only-upgrade cms
# RHEL / Rocky / Alma
sudo dnf upgrade --security -y
# Windows
# PowerShell:
#   winget upgrade --all --silent --accept-package-agreements --accept-source-agreements
# macOS
sudo softwareupdate -i -a -R

After applying the patch

  1. Restart the service or device so the patched binary loads.
  2. Confirm the running version matches the Fixed in row using the verification command below.
  3. Rotate credentials and API keys that the affected service could access if the asset was exposed during the disclosure window.

If you can't patch immediately

Until the patch lands, narrow the attack surface with these runnable controls.

Reduce the attack surface

Restrict network reach to the affected service to the smallest set of hosts that must access it. On Linux:


# Vendor advisory: https://support.sitecore.com/kb?id=kb_article_view&sysparm_article=KB0038556
sudo iptables -A INPUT -p tcp --dport <service-port> -s 10.10.10.0/24 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport <service-port> -j DROP

On Windows:


# Vendor advisory: https://support.sitecore.com/kb?id=kb_article_view&sysparm_article=KB0038556
New-NetFirewallRule -DisplayName "Block CVE-2019-9875 inbound" -Direction Inbound -Action Block -Protocol TCP -LocalPort <service-port>

Mitigations are temporary. Apply the vendor patch as soon as a maintenance window opens.

How to verify the fix worked

Confirm the patched build is the one actually running.

Run the product's --version or about command and compare against the Fixed in row (See vendor advisory). Re-run an authenticated vulnerability scan and confirm the scanner no longer flags CVE-2019-9875.

Also worth doing: pull recent log windows for any indicators of compromise listed in the vendor advisory, and re-run an authenticated vulnerability scan with up-to-date signatures.

Frequently asked questions

Other vulnerabilities in the same area that are worth patching alongside this one:

Is CVE-2019-9875 being exploited in the wild?

Yes. CISA added CVE-2019-9875 to the Known Exploited Vulnerabilities catalog on 2025-03-26. KEV listing means at least one confirmed real-world exploitation report exists.

Do I have to take downtime to patch?

For most Sitecore CMS and Experience Platform (XP) deployments, the patched build needs a service restart or device reboot. HA pairs and clusters can roll the upgrade by patching the standby first, failing over, then patching the former primary.

Will a WAF or IDS rule alone close CVE-2019-9875?

No. Network filters cut down opportunistic scans but they do not remove the flaw. The vendor patch is the only durable fix.

How quickly should I act on CVE-2019-9875?

Within the standard patch cycle if the asset is internal-only. Inside one to two weeks for any internet-facing instance, sooner if compensating controls are not in place.

References

*Assembled from the official vendor advisory, the NVD record, and the CISA KEV listing on 2026-05-25. Always confirm against the vendor advisory before applying changes in production.*