CVE-2021-39153Public exploitNetwork attack vector

Arbitrary code execution via attacker-selected type instantiation

Published Aug 23, 2021 · Updated Aug 4, 2024

Deserialization of untrusted data in XStream before 1.4.18 allows remote attackers to execute arbitrary code through a crafted input stream. During unmarshalling, an uninitialized security framework accepts attacker-selected type information and instantiates a PriorityQueue gadget chain that reaches JavaFX TemplatesImpl bytecode execution. The chain applies to the default blacklist configuration on Java 8 through 14 or with JavaFX installed; a minimal type whitelist blocks it.

CVSS severity8.5
High
EPSS probability4.46%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Deserialization of untrusted data in XStream before 1.4.18 allows remote attackers to execute arbitrary code through a crafted input stream. During unmarshalling, an uninitialized security framework accepts attacker-selected type information and instantiates a PriorityQueue gadget chain that reaches JavaFX TemplatesImpl bytecode execution. The chain applies to the default blacklist configuration on Java 8 through 14 or with JavaFX installed; a minimal type whitelist blocks it.

The record

CVE
CVE-2021-39153
Published
Aug 23, 2021
Updated
Aug 4, 2024
Vendor
XStream
Product
XStream
Classifications
CWE-502
Attack vector
network
Privileges
Unavailable

Timeline

How it unfolded

  1. Aug 23, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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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 privilegesUnavailable in this record.

What is affected?

XStream · XStreamversion=< 1.4.18

Published CVSS scores

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 IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-502Deserialization of Untrusted Data

Public exploit references

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

Technologies

Your stack

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Your stack

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