CVE-2021-39140Public exploitNetwork attack vector

Service hang via cyclic map deserialization

Published Aug 23, 2021 · Updated Aug 4, 2024

Denial of service in XStream 1.4.17 and earlier allows remote authenticated users to hang a processing thread via crafted input. During unmarshalling, XStream instantiates attacker-selected types from stream metadata, and a cyclic SimpleBindings map injected through AnnotationInvocationHandler traps the executing thread in an endless loop. Exposure requires an application to unmarshal attacker-controlled data with the default blacklist configuration; parallel payloads can saturate CPU and interrupt the embedding service.

CVSS severity6.5
Medium
EPSS probability5.92%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

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Summary

What happened

Denial of service in XStream 1.4.17 and earlier allows remote authenticated users to hang a processing thread via crafted input. During unmarshalling, XStream instantiates attacker-selected types from stream metadata, and a cyclic SimpleBindings map injected through AnnotationInvocationHandler traps the executing thread in an endless loop. Exposure requires an application to unmarshal attacker-controlled data with the default blacklist configuration; parallel payloads can saturate CPU and interrupt the embedding service.

The record

CVE
CVE-2021-39140
Published
Aug 23, 2021
Updated
Aug 4, 2024
Vendor
XStream
Product
XStream
Classifications
CWE-502, CWE-835, T1499
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

6.5GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
5.9SUSECVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
6.3NIST National Vulnerability DatabaseAV:N/AC:M/Au:S/C:N/I:N/A:C
6.3NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:N/I:N/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-835Loop with Unreachable Exit Condition ('Infinite Loop')
T1499Endpoint Denial of Service

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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