# CVE-2021-41556: Memory corruption in n/a

> An out-of-bounds read in the Squirrel interpreter allows attackers to execute arbitrary code and escape the sandbox by providing a malicious script.

- **Severity:** Critical 10.0 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 28 Jul 2022
- **Updated:** 29 May 2026
- **Also known as:** DEBIAN-CVE-2021-41556, GHSA-cm28-mc8h-9h49, MGASA-2023-0150, UBUNTU-CVE-2021-41556, openSUSE-SU-2023:0080-1, openSUSE-SU-2024:12611-1

## What is CVE-2021-41556?

CVE-2021-41556 is a critical memory corruption vulnerability in Fedoraproject Fedora, published on 28 Jul 2022. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2021-41556?

It affects 2 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `squirrel` | SUSE:Package Hub 15 SP4 | All versions | 3.0.7-bp154.3.3.1 |
| `squirrel` | openSUSE:Leap 15.4 | All versions | 3.0.7-bp154.3.3.1 |
| `squirrel` | openSUSE:Tumbleweed | All versions | 3.2-1.1 |

Products: Fedoraproject Fedora, Squirrel-Lang Squirrel.

## How do I fix CVE-2021-41556?

Upgrade to a fixed version.

## Is CVE-2021-41556 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-41556 exists.

## Other vulnerabilities in Fedoraproject Fedora

- [CVE-2024-4577](https://insights.sbomify.com/CVE-2024-4577/): PHP-CGI OS Command Injection (critical 9.8, exploited in the wild)
- [CVE-2021-39226](https://insights.sbomify.com/CVE-2021-39226/): Grafana Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2019-5544](https://insights.sbomify.com/CVE-2019-5544/): VMware ESXi and Horizon DaaS OpenSLP Heap-Based Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2024-4947](https://insights.sbomify.com/CVE-2024-4947/): Google Chromium V8 Type Confusion (critical 9.6, exploited in the wild)
- [CVE-2024-4671](https://insights.sbomify.com/CVE-2024-4671/): Google Chromium Visuals Use-After-Free (critical 9.6, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-41556 and fix it if it is affected.

What it is: CVE-2021-41556 is a critical memory corruption vulnerability in Fedoraproject Fedora, published on 28 Jul 2022. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-41556 exists.

Affected product: Fedoraproject Fedora. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-41556/ (Markdown: https://insights.sbomify.com/CVE-2021-41556/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-41556
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-41556
- OSV: https://osv.dev/vulnerability/CVE-2021-41556

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-41556/
Summaries are generated and may contain mistakes; the official description above is the record.