CVE-2021-39144Known exploitationPublic exploitNetwork attack vector

Remote command execution via unsafe unmarshalling

Published Aug 23, 2021 · Updated Oct 21, 2025

Deserialization in XStream before 1.4.18 allows remote authenticated users to execute host commands through a crafted input stream. During unmarshalling, XStream trusts embedded type information and instantiates attacker-selected objects whose gadget chain invokes Runtime.exec. Exposure requires application-supplied untrusted data and the default blacklist; a minimal type allowlist blocks the gadget.

CVSS severity8.5
High
EPSS probability98.12%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Deserialization in XStream before 1.4.18 allows remote authenticated users to execute host commands through a crafted input stream. During unmarshalling, XStream trusts embedded type information and instantiates attacker-selected objects whose gadget chain invokes Runtime.exec. Exposure requires application-supplied untrusted data and the default blacklist; a minimal type allowlist blocks the gadget.

The record

CVE
CVE-2021-39144
Published
Aug 23, 2021
Updated
Oct 21, 2025
Vendor
XStream
Product
XStream
Classifications
CWE-94, CWE-502
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 23, 2021CVE publishedPublication date reported by the CVE source.
  2. Oct 21, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.4.18

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

XStream · XStreamversion=< 1.4.18

Published CVSS scores

8.5NIST NVDCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
8.5GitHubCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsShadowserver observations through Sep 16, 2026. Gaps indicate unavailable data.
Sep 10, 2026Sep 16, 2026
View daily counts
Reporting dayUnique IPs
Sep 10, 20262
Sep 11, 2026Unavailable
Sep 12, 2026Unavailable
Sep 13, 2026Unavailable
Sep 14, 2026Unavailable
Sep 15, 2026Unavailable
Sep 16, 2026Unavailable
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-94Improper Control of Generation of Code ('Code Injection')
CWE-502Deserialization of Untrusted Data

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

See the directory against your own environment.

Your stack

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