# CVE-2021-35513: Cross-site Scripting in Mermaid

> Attackers can execute arbitrary scripts via XSS in Mermaid when the antiscript feature is enabled, affecting applications using this library.

- **Severity:** Medium 6.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 27 Jun 2021
- **Updated:** 4 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-35513, GHSA-4f6x-49g2-99fm, UBUNTU-CVE-2021-35513

## What is CVE-2021-35513?

CVE-2021-35513 is a medium-severity cross-site scripting vulnerability in n/a, published on 27 Jun 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

Mermaid before 8.11.0 allows XSS when the antiscript feature is used.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2021-35513?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `mermaid` | npm | All versions | 8.11.0 |
| `mermaid` | npm | All versions | 8.11.0 |

Products: Mermaid Project Mermaid.

## How do I fix CVE-2021-35513?

Upgrade mermaid to 8.11.0 or later.

## Is CVE-2021-35513 being exploited?

There is no known exploitation of CVE-2021-35513 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2021-43861](https://insights.sbomify.com/CVE-2021-43861/): Incorrect sanitisation function leads to `XSS` (high 7.2)
- [CVE-2026-41150](https://insights.sbomify.com/CVE-2026-41150/): Mermaid Gantt Charts are vulnerable to an Infinite Loop DoS (medium 5.3)
- [CVE-2026-41159](https://insights.sbomify.com/CVE-2026-41159/): Mermaid: Improper sanitization of configuration leads to CSS injection (medium 5.3)
- [CVE-2025-54880](https://insights.sbomify.com/CVE-2025-54880/): Mermaid does not properly sanitize architecture diagram iconText leading to XSS (medium 5.1)
- [CVE-2022-31108](https://insights.sbomify.com/CVE-2022-31108/): Arbitrary `CSS` injection into the generated graph affecting the container HTML in mermaid.js (medium 4.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-35513 and fix it if it is affected.

What it is: CVE-2021-35513 is a medium-severity cross-site scripting vulnerability in n/a, published on 27 Jun 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-35513 in the wild and no public exploit code.

Affected packages and fixed versions:
- mermaid (npm): affected all versions; fixed in 8.11.0
- mermaid (npm): affected all versions; fixed in 8.11.0

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-2021-35513/ (Markdown: https://insights.sbomify.com/CVE-2021-35513/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-35513
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-35513
- OSV: https://osv.dev/vulnerability/CVE-2021-35513

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-35513/
Summaries are generated and may contain mistakes; the official description above is the record.