CVE-2021-39150Public exploitNetwork attack vector

Internal resource access via PriorityQueue unmarshalling

Published Aug 23, 2021 · Updated Aug 4, 2024

Server-side request forgery in XStream before 1.4.18 allows remote authenticated users to request data from internal or local URLs. During XML unmarshalling, attacker-controlled type metadata constructs nested PriorityQueue and JAX-WS objects whose comparison path dereferences an arbitrary URL. Reachability requires Java 8 through 14, untrusted XML input, and the default blacklist rather than a minimal type allowlist.

CVSS severity8.5
High
EPSS probability3.44%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Server-side request forgery in XStream before 1.4.18 allows remote authenticated users to request data from internal or local URLs. During XML unmarshalling, attacker-controlled type metadata constructs nested PriorityQueue and JAX-WS objects whose comparison path dereferences an arbitrary URL. Reachability requires Java 8 through 14, untrusted XML input, and the default blacklist rather than a minimal type allowlist.

The record

CVE
CVE-2021-39150
Published
Aug 23, 2021
Updated
Aug 4, 2024
Vendor
XStream
Product
XStream
Classifications
CWE-918, CWE-502, T1190
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

6.0NIST NVDAV:N/AC:M/Au:S/C:P/I:P/A:P
8.5NIST NVDCVSS: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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-918Server-Side Request Forgery (SSRF)
CWE-502Deserialization of Untrusted Data
T1190Exploit Public-Facing Application

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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