# CVE-2021-32821: Regular expression Denial of Service in MooTools

> Attackers can cause denial of service in MooTools by injecting malicious strings into CSS selectors, exploiting a vulnerable regex parser.

- **Severity:** Medium 6.2 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 3 Jan 2023
- **Updated:** 10 Mar 2025
- **Also known as:** DEBIAN-CVE-2021-32821, GHSA-v63q-hgqc-qvpg, UBUNTU-CVE-2021-32821

## What is CVE-2021-32821?

CVE-2021-32821 is a medium-severity denial of service vulnerability in mootools-core, published on 3 Jan 2023. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

MooTools is a collection of JavaScript utilities for JavaScript developers. All known versions include a CSS selector parser that is vulnerable to Regular Expression Denial of Service (ReDoS). An attack requires that an attacker can inject a string into a CSS selector at runtime, which is quite common with e.g. jQuery CSS selectors. No patches are available for this issue.

Weakness: CWE-1333 (Inefficient Regular Expression Complexity), CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2021-32821?

2 open source packages ship an affected version, including mootools. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `mootools` | npm | All versions to 1.5.2 | None |
| `mootools` | npm | All versions to 1.5.2 | None |

Products: Mootools Mootools.

## How do I fix CVE-2021-32821?

No fix has been published for CVE-2021-32821 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-32821 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-32821 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-32821 and fix it if it is affected.

What it is: CVE-2021-32821 is a medium-severity denial of service vulnerability in mootools-core, published on 3 Jan 2023. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-32821 exists.

Affected packages and fixed versions:
- mootools (npm): affected all versions up to 1.5.2; no fix listed
- mootools (npm): affected all versions up to 1.5.2; no fix listed

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-2021-32821/ (Markdown: https://insights.sbomify.com/CVE-2021-32821/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-32821
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-32821
- OSV: https://osv.dev/vulnerability/CVE-2021-32821

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-32821/
Summaries are generated and may contain mistakes; the official description above is the record.