FedoraOperating system · Fedoraproject
CVE-2021-41556
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedsqclass.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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceAn out-of-bounds read vulnerability exists in sqclass.cpp within the Squirrel scripting language interpreter (versions 2.2.5 and 3.x through 3.1). The flaw allows an attacker to achieve code execution by providing a specially crafted Squirrel script, bypassing sandbox restrictions even when dangerous functions like file system operations are disabled.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
FedoraOperating system
= 35= 36<= 2.2.5>= 3.0, <= 3.1CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Changed
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Verify Squirrel interpreter is installedCheck for squirrel binaries (sq, squirrel) in system paths using 'which sq' or 'which squirrel', or look for squirrel-related packages with your system package manager (e.g., 'rpm -qa | grep -i squirrel' on Fedora)Affected if Squirrel interpreter is found on the system
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Determine installed Squirrel versionRun 'sq -v' or 'squirrel -v' to display version information. If using a library, check the version header or linked library version (lib squirrel.so or squirrel.lib)Affected if Version is 2.2.5 or earlier, or 3.0 through 3.1 inclusive
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Identify if application uses Squirrel as embedded interpreterSearch source code or binaries for squirrel library linkage (e.g., 'ldd <binary>' on Linux, or review application's dependency documentation)Affected if Application links against squirrel library versions 2.2.5 or earlier, or 3.0-3.1
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Confirm if untrusted Squirrel scripts are processedReview application configuration and code to determine if it accepts and executes Squirrel scripts from external or untrusted sources (check for script upload features, user-provided code, or dynamic script loading)Affected if Application executes Squirrel scripts from untrusted input sources
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Check for sandbox mitigation bypass riskVerify whether dangerous functions (file I/O, system calls) have been disabled in the sandbox configuration, since this CVE bypasses such restrictionsAffected if Sandbox restrictions are relied upon to limit script capabilities
A system is affected if it runs Squirrel version 2.2.5 or earlier, or versions 3.0 through 3.1, and processes untrusted Squirrel scripts regardless of sandbox restrictions being in place.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scopedUpgrade Squirrel to the latest version containing the security patch. If immediate patching is not feasible, disable Squirrel script execution from untrusted sources and implement additional isolation layers such as sandboxed containers or VMs.
Squirrel 2.3.0+ or Squirrel 3.2.0+ (depending on which branch is in use)
- 1. Identify the Squirrel version currently in use by checking your application's dependencies or running squirrel --version
- 2. If using Squirrel 2.x (version <= 2.2.5), upgrade to Squirrel 2.3.0 or later
- 3. If using Squirrel 3.x (version 3.0 to 3.1), upgrade to Squirrel 3.2.0 or later
- 4. Rebuild and recompile any applications that embed the Squirrel engine
- 5. Verify the upgrade by running: sq -v (or equivalent version check for your integration)
- 6. Re-test any squirrel scripts that were previously running to ensure functionality is intact
- 7. If using Fedora 35 or 36, ensure the updated squirrel package is obtained from Fedora updates or rebuild from source with the fixed version
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Fedora
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,176.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-41556 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-41556 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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