CVE-2021-21346Public exploitNetwork attack vector

Arbitrary code execution via injected object types

Published Mar 22, 2021 · Updated Aug 3, 2024

Deserialization of untrusted data in XStream before 1.4.16 allows remote attackers to execute arbitrary code through crafted input. During unmarshalling, XStream trusts attacker-controlled type information, instantiates injected object graphs, and triggers a SwingLazyValue chain that performs a JNDI lookup to load remote code. Exploitation requires an application to process the stream with the default blacklist; a minimal type whitelist blocks the injected classes.

CVSS severity6.1
Medium
EPSS probability76.37%
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 1.4.16 allows remote attackers to execute arbitrary code through crafted input. During unmarshalling, XStream trusts attacker-controlled type information, instantiates injected object graphs, and triggers a SwingLazyValue chain that performs a JNDI lookup to load remote code. Exploitation requires an application to process the stream with the default blacklist; a minimal type whitelist blocks the injected classes.

The record

CVE
CVE-2021-21346
Published
Mar 22, 2021
Updated
Aug 3, 2024
Vendor
XStream
Product
XStream
Classifications
CWE-502, CWE-434, T1203
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

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=< 1.4.16

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

XStream · XStreamversion=< 1.4.16

Published CVSS scores

6.1GitHub, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:H/A:N
9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-502Deserialization of Untrusted Data
CWE-434Unrestricted Upload of File with Dangerous Type
T1203Exploitation for Client Execution

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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