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Vulnerability record · CVE-2021-21345 · published 23 March 2021

CVE-2021-21345: XStream deserialization allows remote command execution

NNetapp · Oncommand Insight

XStream before 1.4.16 deserializes untrusted XML without adequate type restrictions, allowing code injection and OS command execution. The flaw is a deserialization of untrusted data issue (CWE-502) that also enables code and command injection. Systems relying on XStream's default blacklist rather than a minimal whitelist are exposed.

9.9 CVSS 3.1 Critical EPSS 72% · top 0.6% CWE-94 · Code injectionCWE-502 · Deserialization of untrusted data
9.9CVSS 3.1 base score, v2 6.5
72%EPSS exploitation probability, 30 days
NoNot in CISA KEV
16Affected product versions listed by NVD
32References, 2 tagged exploit
17 Jun 2026Last modified by NVD

Description

XStream is a Java library to serialize objects to XML and back again. In XStream before version 1.4.16, there is a vulnerability which may allow a remote attacker who has sufficient rights to execute commands of the host only by manipulating the processed input stream. No user is affected, who followed the recommendation to setup XStream's security framework with a whitelist limited to the minimal required types. If you rely on XStream's default blacklist of the Security Framework, you will have to use at least version 1.4.16.

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Automated analysis

Generated by VULONE's analysis model from the NVD record, CISA KEV and EPSS data on 18 September 2026. Confidence: high.

critical priorityCVSS 9.9 with network reachability, low privileges, and high EPSS indicate severe risk of remote code execution.

What it is

XStream before 1.4.16 deserializes untrusted XML without adequate type restrictions, allowing code injection and OS command execution. The flaw is a deserialization of untrusted data issue (CWE-502) that also enables code and command injection. Systems relying on XStream's default blacklist rather than a minimal whitelist are exposed.

Impact

An attacker with sufficient rights can execute arbitrary commands on the host by manipulating the processed input stream. This can lead to full compromise of the application and underlying system.

Attack surface

Reachable over the network via crafted XML input to an XStream deserialization endpoint. The CVSS vector indicates low privileges are required and no user interaction is needed.

Exploitation

Not listed in CISA KEV, but EPSS is very high (0.72324, 99.4th percentile) and a public exploit reference exists. No ransomware groups are documented as using it.

What to do

  • Upgrade XStream to version 1.4.16 or later.
  • Configure XStream's security framework with a whitelist limited to the minimal required types.
  • Apply vendor patches for affected products (Oracle, NetApp, Debian, Fedora, Apache ActiveMQ, JMeter).
  • Avoid deserializing untrusted XML input where possible.

Detection

  • Monitor for XML payloads containing XStream-specific class or method references in deserialization endpoints.
  • Alert on unexpected child processes spawned by Java application servers.
  • Review application logs for deserialization errors or unusual class loading.

This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.

Affected products

16 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
http://x-stream.github.io/changes.html#1.4.16 Release NotesThird Party Advisory
https://github.com/x-stream/xstream/security/advisories/GHSA-hwpc-8xqv-jvj4 Third Party Advisory
https://lists.apache.org/thread.html/r8244fd0831db894d5e89911ded9c72196d395a90ae655414d23ed0dd%40%3Cusers.activemq.apach Issue TrackingMailing ListThird Party Advisory
https://lists.apache.org/thread.html/r9ac71b047767205aa22e3a08cb33f3e0586de6b2fac48b425c6e16b0%40%3Cdev.jmeter.apache.or Issue TrackingMailing ListThird Party Advisory
https://lists.debian.org/debian-lts-announce/2021/04/msg00002.html Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/22KVR6B5IZP3BGQ3HPWIO2F Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PVPHZA7VW2RRSDCOIPP2W6O Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QGXIU3YDPG6OGTDHMBLAFN7 Mailing ListThird Party Advisory
https://security.netapp.com/advisory/ntap-20210430-0002/ Third Party Advisory
https://www.debian.org/security/2021/dsa-5004 Mailing ListThird Party Advisory
https://www.oracle.com//security-alerts/cpujul2021.html Third Party Advisory
https://www.oracle.com/security-alerts/cpuApr2021.html PatchThird Party Advisory
https://www.oracle.com/security-alerts/cpujan2022.html PatchVendor Advisory
https://www.oracle.com/security-alerts/cpuoct2021.html Third Party Advisory
https://x-stream.github.io/CVE-2021-21345.html ExploitThird Party Advisory
https://x-stream.github.io/security.html#workaround MitigationThird Party Advisory
http://x-stream.github.io/changes.html#1.4.16 Release NotesThird Party Advisory
https://github.com/x-stream/xstream/security/advisories/GHSA-hwpc-8xqv-jvj4 Third Party Advisory
https://lists.apache.org/thread.html/r8244fd0831db894d5e89911ded9c72196d395a90ae655414d23ed0dd%40%3Cusers.activemq.apach Issue TrackingMailing ListThird Party Advisory
https://lists.apache.org/thread.html/r9ac71b047767205aa22e3a08cb33f3e0586de6b2fac48b425c6e16b0%40%3Cdev.jmeter.apache.or Issue TrackingMailing ListThird Party Advisory
https://lists.debian.org/debian-lts-announce/2021/04/msg00002.html Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/22KVR6B5IZP3BGQ3HPWIO2F Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PVPHZA7VW2RRSDCOIPP2W6O Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QGXIU3YDPG6OGTDHMBLAFN7 Mailing ListThird Party Advisory
https://security.netapp.com/advisory/ntap-20210430-0002/ Third Party Advisory
https://www.debian.org/security/2021/dsa-5004 Mailing ListThird Party Advisory
https://www.oracle.com//security-alerts/cpujul2021.html Third Party Advisory
https://www.oracle.com/security-alerts/cpuApr2021.html PatchThird Party Advisory
https://www.oracle.com/security-alerts/cpujan2022.html PatchVendor Advisory
https://www.oracle.com/security-alerts/cpuoct2021.html Third Party Advisory
https://x-stream.github.io/CVE-2021-21345.html ExploitThird Party Advisory
https://x-stream.github.io/security.html#workaround MitigationThird Party Advisory

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Source: NIST National Vulnerability Database (record CVE-2021-21345), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.