CVE-2021-29505Public exploitNetwork attack vector

Remote command execution via unsafe object reconstruction

Published May 28, 2021 · Updated May 29, 2025

Deserialization in XStream 1.4.16 and earlier allows remote authenticated users to execute host commands through a crafted input stream. During unmarshalling, XStream trusts embedded type information and instantiates attacker-selected Java object graphs whose gadget chain executes a local command. The flaw affects out-of-the-box instances with an uninitialized security framework; a minimal type whitelist blocks the documented chain.

CVSS severity7.5
High
EPSS probability77.23%
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 1.4.16 and earlier allows remote authenticated users to execute host commands through a crafted input stream. During unmarshalling, XStream trusts embedded type information and instantiates attacker-selected Java object graphs whose gadget chain executes a local command. The flaw affects out-of-the-box instances with an uninitialized security framework; a minimal type whitelist blocks the documented chain.

The record

CVE
CVE-2021-29505
Published
May 28, 2021
Updated
May 29, 2025
Vendor
XStream
Product
XStream
Classifications
CWE-94, CWE-502
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 28, 2021CVE publishedPublication date reported by the CVE source.
  2. May 29, 2025Record 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=< 1.4.17

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

XStream · XStreamversion=< 1.4.17

Published CVSS scores

7.5GitHubCVSS:3.1/AV:N/AC:H/PR:L/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.

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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
Privilegesauthenticated
Known exploitationUnconfirmed
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.

Technologies

Your stack

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Your stack

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