Hazard

Is CVE-2021-39144 being exploited?

Weaponised and widely attempted

Reliable public exploit code exists, or mass exploitation attempts are probable. Patch inside days, not weeks.

XStream Remote Code Execution Vulnerability

XStream · XStream

CVSS 8.5 EPSS 98% no public exploit indexed Fix deadline passed 31 March 2023

What it is

XStream contains a remote code execution vulnerability that allows an attacker to manipulate the processed input stream and replace or inject objects that result in the execution of a local command on the server. This vulnerability can affect multiple products, including but not limited to VMware Cloud Foundation.

Why we say that

  • EPSS puts exploitation in the next 30 days at 98%
  • CISA's federal remediation deadline (2023-03-31) has passed
  • Listed in the CISA Known Exploited Vulnerabilities catalogue

Every line above comes from a named public source. Where the evidence is thin, we say so rather than inventing confidence — see methodology.

What to do

Apply updates per vendor instructions.

What it costs when this goes wrong

This is where UK enforcement meets the vulnerability record. Where an unfixed vulnerability leads to a breach, the ICO treats it as a security failure under UK GDPR. Recent cases:

All UK cases caused by unpatched software →