CVE-2021-41556

CRITICALNVD 10.010.0—
EchelonGraph scoreMEDIUM confidence

Score 10.0 from GitHub Security Advisory (severity: CRITICAL) published 2022-07-29. NVD baseline CVSS 10.0; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
Elevated
10.0
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 2%CVSS: 10.0Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

sqclass.cpp in Squirrel through 2.2.5 and 3.x through 3.1 allows an out-of-bounds read (in the core interpreter) that can lead to Code Execution. If a victim executes an attacker-controlled squirrel script, it is possible for the attacker to break out of the squirrel script sandbox even if all dangerous functionality such as File System functions has been disabled. An attacker might abuse this bug to target (for example) Cloud services that allow customization via SquirrelScripts, or distribute malware through video games that embed a Squirrel Engine.

CVSS v3
10.0
EG Score
10.0(medium)
EG Risk
76(Attend)
EG Risk 76/100SSVC: Attend

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity100% × 45%
Exploitation40% × 40%
Automatability100% × 15%
Action: Remediate soon — notable exploitation risk.
EPSS
80.4%
KEV
Not listed

Published

July 28, 2022

Last Modified

May 29, 2026

Advisory Details (5)

Auto-updated Jul 21, 2026
Patch available. Sources: github_commit.
generic

[SECURITY] Fedora 36 Update: squirrel-2.2.5-25.fc36 - package-announce - Fedora mailing-lists

https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/M3FQILX7UUEERSDPMZP3MKGTMY2E7ESU/
generic

[SECURITY] Fedora 35 Update: squirrel-2.2.5-25.fc35 - package-announce - Fedora mailing-lists

https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BV7SJJ44AGAX4ILIVPREIXPJ2GOG3FKV/
github_commit Patch Available

commit 23a062065871 (albertodemichelis/squirrel)

Patch available: albertodemichelis/squirrel v3.2 (contains commit 23a062065871)

https://github.com/albertodemichelis/squirrel/commit/23a0620658714b996d20da3d4dd1a0dcf9b0bd98
generic Patch Available

Squirrel Sandbox Escape allows Code Execution in Games and Cloud Services | Sonar

https://blog.sonarsource.com/squirrel-vm-sandbox-escape/
generic

Squirrel - The Programming Language

http://www.squirrel-lang.org/#download

Vendor Advisories for CVE-2021-41556(1)

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

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 12× in last 7d / 46× 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.

Showing the most recent 100 of 105 total refreshes for this CVE.

  1. 2026-07-24 14:15 UTCEPSS rescore
  2. 2026-07-23 14:16 UTCEPSS rescore
  3. 2026-07-23 02:04 UTCEG score recompute
  4. 2026-07-22 22:51 UTCEG score recompute
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  13. 2026-07-17 00:04 UTCOSV refresh
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  1. 2026-07-07 13:43 UTCEPSS rescore
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  14. 2026-06-28 22:32 UTCOSV refresh
  15. 2026-06-28 14:05 UTCEPSS rescore
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  26. 2026-06-21 14:55 UTCEPSS rescore
  27. 2026-06-21 01:58 UTCEPSS rescore
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  43. 2026-06-12 23:10 UTCEPSS rescore
  44. 2026-06-11 18:25 UTCOSV refresh
  45. 2026-06-11 13:58 UTCEPSS rescore
  46. 2026-06-11 13:58 UTCEPSS rescore
  47. 2026-06-10 22:16 UTCEPSS rescore
  48. 2026-06-10 22:16 UTCEPSS rescore
  49. 2026-06-10 13:20 UTCEPSS rescore
  50. 2026-06-08 14:15 UTCEPSS rescore
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  52. 2026-06-07 15:23 UTCEPSS rescore
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  54. 2026-06-06 13:46 UTCEPSS rescore
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Frequently asked(5)

What is CVE-2021-41556?
CVE-2021-41556 is a critical vulnerability published on July 28, 2022. sqclass.cpp in Squirrel through 2.2.5 and 3.x through 3.1 allows an out-of-bounds read (in the core interpreter) that can lead to Code Execution. If a victim executes an attacker-controlled squirrel script, it is possible for the attacker to break out of the squirrel script sandbox even if all…
When was CVE-2021-41556 disclosed?
CVE-2021-41556 was first published in the National Vulnerability Database on July 28, 2022, with the most recent update on May 29, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-41556 actively exploited?
CVE-2021-41556 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 80.4% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-41556?
CVE-2021-41556 has a CVSS v3 base score of 10.0 (NVD).
How do I remediate CVE-2021-41556?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-41556, 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

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