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CVE-2019-9875

From Exploited flaws, HARD’s guide to the flaws being used in attacks · Checked
This article is about a flaw in Sitecore CMS and Experience Platform (XP). For every flaw being used in attacks, see Exploited flaws; for Sitecore’s, see Sitecore flaws being used in attacks.

CVE-2019-9875 is a security flaw in Sitecore CMS and Experience Platform (XP). Someone who already has a way in can use Sitecore CMS and Experience Platform (XP) to run their own code. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 26 Mar 2025.[1]

Sitecore CMS and Experience Platform (XP) is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Sitecore has published a fix or advice.

Description

CISA calls it a deserialization in Sitecore CMS and Experience Platform (XP). In its words: “Sitecore CMS and Experience Platform (XP) contain a deserialization vulnerability in the Sitecore.Security.AntiCSRF module that allows an authenticated attacker to execute arbitrary code by sending a serialized .NET object in the HTTP POST parameter __CSRFTOKEN.”[1]

The underlying weakness is deserialization of untrusted data (CWE-502), in MITRE’s list of common software weaknesses.[2]

It scores 8.8 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by NVD using CVSS 3.1.[2]

Affected versions

NVD’s record doesn’t list version ranges for it; Sitecore’s advisory has them[3]. CISA names the product as Sitecore CMS and Experience Platform (XP).

Most families won’t have Sitecore CMS and Experience Platform (XP); it’s for whoever looks after IT at work.

Exploitation

CISA added it to its catalog of known exploited vulnerabilities on 26 Mar 2025, 2,126 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 16 Apr 2025 to fix it.[1]

FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 25%. That’s in the top 3% of the flaws it scores.[4]

CISA assesses it as not automatable: each attack takes some work.

CISA doesn’t say who was attacked, or how.

Fix

Sitecore has published a fix or advice.[3] CISA’s required action: “Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.”[1]

  1. Check whether you use it.Sitecore CMS and Experience Platform (XP) is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
  2. Send this page to your IT person.Ask them to confirm it’s fixed, or not in use. CISA gave US government agencies until 16 Apr 2025 to fix it.
  3. If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.

You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.

Timeline

DateEvent
The flaw is made public in the National Vulnerability Database, with a severity score of 8.8.[2]
CISA adds it to its catalog of flaws known to be used in attacks.[1]
CISA’s deadline for US government agencies to fix it.[1]
FIRST puts the odds of it being used in attacks in the next 30 days at 25%.[4]

See also

Other Sitecore CMS and Experience Platform (XP) flaws

Other Sitecore flaws

  • CVE-2025-53690, Sitecore products: deserialization of untrusted data ·
  • CVE-2021-42237, Sitecore XP: remote command execution ·

Other deserialization of untrusted data flaws

  • CVE-2021-23758, Ajax.NET Professional: deserialization of untrusted data ·
  • CVE-2026-63077, JetBrains TeamCity: deserialization of untrusted data ·
  • CVE-2026-50522, Microsoft SharePoint: deserialization of untrusted data ·
  • CVE-2026-58644, Microsoft SharePoint: deserialization of untrusted data ·
  • CVE-2026-45659, Microsoft SharePoint Server: deserialization of untrusted data ·

Added the same day

  • CVE-2019-9874, Sitecore CMS and Experience Platform (XP): deserialization ·

Every Sitecore flaw on CISA’s list · Everything added in March 2025

References

  1. ^ Cybersecurity and Infrastructure Security Agency. “Sitecore CMS and Experience Platform (XP) Deserialization Vulnerability”. Known Exploited Vulnerabilities Catalog, added 26 Mar 2025.
  2. ^ National Institute of Standards and Technology. “CVE-2019-9875 Detail”. National Vulnerability Database, published 31 May 2019.
  3. ^ Sitecore. Advisories and fixes: support.sitecore.com, dev.sitecore.net.
  4. ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.254, percentile 97.9, 31 Oct 2026.
  5. CVE Program. “CVE-2019-9875”. The official CVE record.

This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.