A Server-Side Forgery Request can be activated unmarshalling with XStream to access data streams from an arbitrary URL referencing a resource in an intranet or the local host

Exploitation

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

CVSS

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

EPSS

• CVE-2021-21342: 49.99% estimated exploitation activity in the next 30 days; percentile 98.90 (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 processed stream at unmarshalling time contains type information to recreate the formerly written objects. XStream creates therefore new instances based on these type information. An attacker can manipulate the processed input stream and replace or inject objects, that result in a server-side forgery request. No user is affected, who followed the recommendation to setup XStream's security framework with a whitelist limited to the minimal required types. Patches If you rely on XStream's default blacklist of the Security Framework, you will have to use at least version 1.4.16 Workarounds See workarounds for the different versions covering all CVEs. References See full information about the nature of the vulnerability and the steps to reproduce it in XStream's documentation for CVE-2021-21342. Credits 钟潦贵 (Liaogui Zhong) found and reported the issue to XStream and provided the required information to reproduce it. For more information If you have any questions or comments…

Published by the source

22 Mar 2021, 23:28 UTC

Last modified by the source

9 Mar 2023, 21:21 UTC

Source last checked

26 Oct 2026, 16:11 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-hvv8-336g-rx3m

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# Patch Next advisory brief: CVE-2021-21342

Advisory: A Server-Side Forgery Request can be activated unmarshalling with XStream to access data streams from an arbitrary URL referencing a resource in an intranet or the local host
IDs: CVE-2021-21342, GHSA-hvv8-336g-rx3m
Record: https://patchnext.com/advisories/cve-2021-21342 (revision 1, source checked 26 Oct 2026, 16:11 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
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 1.4.16. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven com.thoughtworks.xstream:xstream: affected < 1.4.16; fixed in 1.4.16

## 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-hvv8-336g-rx3m (GitHub-reviewed advisory GHSA-hvv8-336g-rx3m lists affected ranges: Maven com.thoughtworks.xstream:xstream >=0 <1.4.16)

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