Threats / XStream / CVE-2021-39144
CVE-2021-39144
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-06-22
XStream vulnerability
XStream deserializes untrusted data, allowing remote code execution through object injection. Attackers can manipulate input streams to execute arbitrary commands on affected servers.
Verdict
Today item — known-exploited.
An attacker exploits unsafe deserialization in XStream to inject malicious objects into the processing stream, achieving remote code execution and command execution on the target system. This vulnerability is actively exploited in the wild.
01
Is it exploitable?
— the evidence, ranked above the scoreReported exploitation
376 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2023-03-10).
Probability (EPSS)
EPSS 0.9851 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
Affected: XStream, XStream. Confirm exact fixed builds in the vendor advisory.
Weakness (CWE)
Mapped to CWE-94 Code Injection, CWE-502 Deserialization of Untrusted Data — weakness family: Injection.CWE assignment from the public NVD record; the weakness class drives how the flaw is exploited.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I craft a malicious serialized object and send it to an application using XStream for deserialization.
Business
The organization's server executes arbitrary commands under the application's privileges, compromising system integrity.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I manipulate the input stream to replace legitimate objects with gadget chains that trigger code execution.
Business
Attackers gain persistent access to infrastructure, enabling data theft, lateral movement, and operational disruption.
3
Lateral reach — past segmentation narrative 3
Attacker
I leverage the remote code execution to establish a foothold and escalate privileges within the target environment.
Business
The organization faces potential complete system compromise, regulatory violations, and reputational damage from security breach.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05