Denial of Service by injecting highly recursive collections or maps in XStream

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2021-43859: 7.93% estimated exploitation activity in the next 30 days; percentile 94.74 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact The vulnerability 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. Patches 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. Workarounds The attack uses the hash code implementation for collections and maps to force an exponential calculation time due to highly recursive structures with in the collection or map. Following types of the Java runtime are affected in Java versions available in December 2021: - java.util.HashMap - java.util.HashSet - java.util.Hashtable - java.util.LinkedHashMap - java.util.LinkedHashSet - java.util.Stack (older Java revisions only) - java.util.Vector (older Java revisions only) - Other third party collection implementations that use their element's hash code may also be affected If your…

Published by the source

1 Feb 2022, 00:48 UTC

Last modified by the source

4 Nov 2025, 16:34 UTC

Source last checked

26 Oct 2026, 16:40 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-rmr5-cpv2-vgjf

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# Patch Next advisory brief: CVE-2021-43859

Advisory: Denial of Service by injecting highly recursive collections or maps in XStream
IDs: CVE-2021-43859, GHSA-rmr5-cpv2-vgjf
Record: https://patchnext.com/advisories/cve-2021-43859 (revision 1, source checked 26 Oct 2026, 16:40 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: com.thoughtworks.xstream:xstream 1.4.19. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven com.thoughtworks.xstream:xstream: affected < 1.4.19; fixed in 1.4.19

## Suggested inspection (read-only)
- Maven com.thoughtworks.xstream:xstream: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on com.thoughtworks.xstream:xstream.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-rmr5-cpv2-vgjf (GitHub-reviewed advisory GHSA-rmr5-cpv2-vgjf lists affected ranges: Maven com.thoughtworks.xstream:xstream >=0 <1.4.19)

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