CVE-2021-39139Public exploitNetwork attack vector

Remote code execution via unsafe type instantiation

Published Aug 23, 2021 · Updated Aug 4, 2024

Deserialization in XStream 1.4.17 and earlier allows remote authenticated users to execute arbitrary code through a manipulated input stream. During unmarshalling, XStream trusts attacker-controlled type metadata and instantiates an injected Xalan TemplatesImpl gadget that executes supplied bytecode. Exposure requires an application path that unmarshals the input and either the default blacklist with JDK 1.7u21 or earlier or an external Xalan; a minimal type whitelist blocks the chain.

CVSS severity8.8
High
EPSS probability4.54%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Deserialization in XStream 1.4.17 and earlier allows remote authenticated users to execute arbitrary code through a manipulated input stream. During unmarshalling, XStream trusts attacker-controlled type metadata and instantiates an injected Xalan TemplatesImpl gadget that executes supplied bytecode. Exposure requires an application path that unmarshals the input and either the default blacklist with JDK 1.7u21 or earlier or an external Xalan; a minimal type whitelist blocks the chain.

The record

CVE
CVE-2021-39139
Published
Aug 23, 2021
Updated
Aug 4, 2024
Vendor
XStream
Product
XStream
Classifications
CWE-502, CWE-434
Attack vector
network
Privileges
authenticated

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 privilegesauthenticated

What is affected?

XStream · XStreamversion=< 1.4.18

Published CVSS scores

8.8NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
6.5NVDAV:N/AC:L/Au:S/C:P/I:P/A:P
8.5Amazon LinuxCVSS: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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-502Deserialization of Untrusted Data
CWE-434Unrestricted Upload of File with Dangerous Type

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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