# CVE-2021-21306: Denial of Service in Marked

> Attackers can cause denial of service in applications using the Marked library by submitting specially crafted markdown input.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 Feb 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-4r62-v4vq-hr96

## What is CVE-2021-21306?

CVE-2021-21306 is a medium-severity denial of service vulnerability in markedjs marked, published on 8 Feb 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Marked is an open-source markdown parser and compiler (npm package "marked"). In marked from version 1.1.1 and before version 2.0.0, there is a Regular expression Denial of Service vulnerability. This vulnerability can affect anyone who runs user generated code through marked. This vulnerability is fixed in version 2.0.0.

Weakness: CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2021-21306?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `marked` | npm | From 1.1.1 | 2.0.0 |
| `marked` | npm | From 1.1.1 | 2.0.0 |

Products: Marked Project Marked.

## How do I fix CVE-2021-21306?

Upgrade marked to 2.0.0 or later.

## Is CVE-2021-21306 being exploited?

There is no known exploitation of CVE-2021-21306 in the wild and no public exploit code.

## Other vulnerabilities in markedjs marked

- [CVE-2026-41680](https://insights.sbomify.com/CVE-2026-41680/): Marked: OOM Denial of Service via Infinite Recursion in marked Tokenizer (high 8.7)
- [CVE-2017-16114](https://insights.sbomify.com/CVE-2017-16114/): Regular Expression Denial of Service in marked (high 7.5)
- [CVE-2018-25110](https://insights.sbomify.com/CVE-2018-25110/): Regular Expression Denial of Service (ReDoS) in markedjs/marked (medium 6.9)
- [CVE-2014-3743](https://insights.sbomify.com/CVE-2014-3743/): Multiple Content Injection Vulnerabilities in marked (medium 6.1)
- [CVE-2016-10531](https://insights.sbomify.com/CVE-2016-10531/): Sanitization bypass using HTML Entities in marked (medium 6.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-21306 and fix it if it is affected.

What it is: CVE-2021-21306 is a medium-severity denial of service vulnerability in markedjs marked, published on 8 Feb 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-21306 in the wild and no public exploit code.

Affected packages and fixed versions:
- marked (npm): affected from 1.1.1; fixed in 2.0.0
- marked (npm): affected from 1.1.1; fixed in 2.0.0

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-2021-21306/ (Markdown: https://insights.sbomify.com/CVE-2021-21306/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21306
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21306
- OSV: https://osv.dev/vulnerability/CVE-2021-21306

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-21306/
Summaries are generated and may contain mistakes; the official description above is the record.