Known exploited · XStream

CVE-2021-39144: XStream Remote Code Execution Vulnerability

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.

Added March 10, 2023Due March 31, 2023CISA KEV catalog 2026.10.01

Vendor: XStream
Product: XStream
Added to KEV: March 10, 2023
CISA due date: March 31, 2023
Ransomware use: Unknown
Weakness: CWE-94: Improper Control of Generation of Code ('Code Injection'), CWE-502: Deserialization of Untrusted Data

What CISA requires

Apply updates per vendor instructions.

Forensic triage

What to do now

Find every instance of XStream you run, including the forgotten ones, and check its version against the vendor advisory.
Apply the vendor's fix or mitigation, before March 31, 2023 if you are bound by CISA's deadline, sooner if it faces the internet.
Assume it was tried against you already: look for signs of exploitation from the date it was added, not from the day you patched.
Until every instance is patched, block the attack at the edge: a WAF in blocking mode stops PHP and Node.js code injection payloads.

References

CVE-2021-39144 in the National Vulnerability Database

The Dome

Block it at the edge while you patch

The Dome's WAF runs the OWASP Core Rule Set in blocking mode and stops PHP and Node.js code injection payloads before they reach your application.

See the Dome

T Academy

Train the engineers who fix it

Security engineering on real hosts in the browser, every objective checked on the machine. The first two lessons of Linux 1 are free.

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Source: CISA Known Exploited Vulnerabilities Catalog (public domain), catalog version 2026.10.01.