CVE-2021-21350Network attack vector

Remote code execution via unsafe deserialization

Published Mar 22, 2021 · Updated Aug 3, 2024

XStream before 1.4.16 allows remote attackers to execute arbitrary code by manipulating the processed input stream. XStream unmarshals attacker-controlled XML or other supported data into Java objects while relying on an unsafe blacklist of types, permitting gadget classes to execute in the hosting application. Exploitation requires a remotely reachable application that feeds attacker-controlled data to XStream; a restrictive type whitelist prevents the affected path.

CVSS severity5.3
Medium
EPSS probability15.23%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

XStream before 1.4.16 allows remote attackers to execute arbitrary code by manipulating the processed input stream. XStream unmarshals attacker-controlled XML or other supported data into Java objects while relying on an unsafe blacklist of types, permitting gadget classes to execute in the hosting application. Exploitation requires a remotely reachable application that feeds attacker-controlled data to XStream; a restrictive type whitelist prevents the affected path.

The record

CVE
CVE-2021-21350
Published
Mar 22, 2021
Updated
Aug 3, 2024
Vendor
XStream
Product
XStream
Classifications
CWE-502, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 22, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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=< 1.4.16

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

XStream · XStreamversion=< 1.4.16

Published CVSS scores

5.3GitHub CNACVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N

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.

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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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-502Deserialization of Untrusted Data
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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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