CVE-2021-21351

MEDIUMNVD 5.49.0▲
EchelonGraph scoreHIGH confidence

Score elevated to 9.0 because EPSS predicts 92% probability of exploitation within the next 30 days (top 0.3% of all CVEs). NVD baseline CVSS 5.4 retained for reference. Confidence: see factors.

Triggered by: EPSS exploit prediction ≥85%
Sources: epss, nvd
Elevated
5.4
EchelonGraph verdictPatch this weekExploitation is likely or a public exploit exists.
  • High exploitation likelihood — EPSS 82%
CISA-KEV: Not listedEPSS: 82%CVSS: 5.4Exploit: NoneExposed: 0

A fix is available — apply it.

XStream is a Java library to serialize objects to XML and back again. In XStream before version 1.4.16, there is a vulnerability may allow a remote attacker to load and execute arbitrary code from a remote 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 v3
5.4
EG Score
9.0(high)
EPSS
99.6%
KEV
Not listed

Published

March 23, 2021

Last Modified

May 23, 2025

References (30)

Vendor Advisories for CVE-2021-21351(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(5)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntulibxstream-java (1.4.15-1ubuntu0.1) @ hirsute2026-05-26ubuntu
ubuntulibxstream-java (1.4.8-1ubuntu0.1+esm3) @ xenial2026-05-26ubuntu
redhatxstream2021-12-14redhat
redhatpatch2021-12-02redhat
redhatpatch2021-11-23redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(1 across 1 ecosystem)
Maven(1)
PackageVulnerable rangeFixed inDependents
com.thoughtworks.xstream:xstream0.1 ... 1.4.9 (40 versions)1.4.16—

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Additional Vendor Advisories

(7)

Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.

Data Freshness Timeline

(refreshed 1× in last 7d / 19× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-09 19:07 UTCEPSS rescore
  2. 2026-07-05 02:28 UTCEPSS rescore
  3. 2026-07-05 02:28 UTCEPSS rescore
  4. 2026-07-04 06:29 UTCEPSS rescore
  5. 2026-07-04 06:29 UTCEPSS rescore
  6. 2026-07-01 15:03 UTCEPSS rescore
  7. 2026-07-01 06:48 UTCOSV refresh
  8. 2026-06-29 14:04 UTCEPSS rescore
  9. 2026-06-29 14:04 UTCEPSS rescore
  10. 2026-06-28 04:54 UTCEPSS rescore
  11. 2026-06-28 04:54 UTCEPSS rescore
  12. 2026-06-25 13:48 UTCEPSS rescore
  13. 2026-06-25 13:48 UTCEPSS rescore
  14. 2026-06-23 21:31 UTCEPSS rescore
  15. 2026-06-23 21:31 UTCEPSS rescore
  16. 2026-06-15 17:46 UTCEPSS rescore
  17. 2026-06-13 11:13 UTCOSV refresh
  18. 2026-06-12 23:10 UTCEPSS rescore
  19. 2026-06-12 23:10 UTCEPSS rescore
  20. 2026-06-10 22:16 UTCEPSS rescore
  21. 2026-06-10 22:16 UTCEPSS rescore
  22. 2026-06-06 13:46 UTCEPSS rescore
  23. 2026-06-06 13:46 UTCEPSS rescore
  24. 2026-06-06 13:46 UTCEPSS rescore
  25. 2026-06-05 22:45 UTCEPSS rescore
Show 7 more
  1. 2026-06-05 22:45 UTCEPSS rescore
  2. 2026-06-02 20:11 UTCEPSS rescore
  3. 2026-06-02 20:11 UTCEPSS rescore
  4. 2026-05-29 13:42 UTCEPSS rescore
  5. 2026-05-27 13:39 UTCEPSS rescore
  6. 2026-05-26 19:32 UTCEG score recompute
  7. 2026-05-26 19:32 UTCVendor advisory

Publicly available exploits

(1 reference)

Working exploit code is in the public domain. Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

  • Nucleihttp/cves/2021/CVE-2021-21351.yaml
    First seen Jan 1, 2021

    XStream <1.4.16 - Remote Code Execution

    Open source ↗

Related CVEs(same vendor + same CWE)

Frequently asked(5)

What is CVE-2021-21351?
CVE-2021-21351 is a medium vulnerability published on March 23, 2021. XStream is a Java library to serialize objects to XML and back again. In XStream before version 1.4.16, there is a vulnerability may allow a remote attacker to load and execute arbitrary code from a remote host only by manipulating the processed input stream. No user is affected, who followed the…
When was CVE-2021-21351 disclosed?
CVE-2021-21351 was first published in the National Vulnerability Database on March 23, 2021, with the most recent update on May 23, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-21351 actively exploited?
CVE-2021-21351 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 99.6% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-21351?
CVE-2021-21351 has a CVSS v3 base score of 5.4 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 9.0.
How do I remediate CVE-2021-21351?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-21351, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2021-21351

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