# CVE-2021-39175: XSS vector in slide mode speaker-view

> An unauthenticated attacker can inject arbitrary JavaScript into HedgeDoc slide speaker-notes, enabling code execution in victim browsers.

- **Severity:** High 8.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/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:** No
- **Published:** 30 Aug 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-j748-779h-9697

## What is CVE-2021-39175?

CVE-2021-39175 is a high-severity cross-site scripting vulnerability in hedgedoc, published on 30 Aug 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

HedgeDoc is a platform to write and share markdown. In versions prior to 1.9.0, an unauthenticated attacker can inject arbitrary JavaScript into the speaker-notes of the slide-mode feature by embedding an iframe hosting the malicious code into the slides or by embedding the HedgeDoc instance into another page. The problem is patched in version 1.9.0. There are no known workarounds aside from upgrading.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation), CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component), CWE-346 (Origin Validation Error)

## Which versions are affected by CVE-2021-39175?

It affects 1 product.


Products: Hedgedoc Hedgedoc.

## How do I fix CVE-2021-39175?

No fix has been published for CVE-2021-39175 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-39175 being exploited?

There is no known exploitation of CVE-2021-39175 in the wild and no public exploit code.

## Other vulnerabilities in hedgedoc

- [CVE-2021-29475](https://insights.sbomify.com/CVE-2021-29475/): PDF export allows arbitrary file reads (critical 10.0)
- [CVE-2020-26287](https://insights.sbomify.com/CVE-2020-26287/): Stored XSS in mermaid diagrams (high 8.7)
- [CVE-2021-29503](https://insights.sbomify.com/CVE-2021-29503/): Improper Neutralization of Script-Related HTML Tags in Notes (high 8.1)
- [CVE-2020-26286](https://insights.sbomify.com/CVE-2020-26286/): Arbitary file upload (high 7.5)
- [CVE-2021-21259](https://insights.sbomify.com/CVE-2021-21259/): Stored XSS in slide mode (high 7.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-39175 and fix it if it is affected.

What it is: CVE-2021-39175 is a high-severity cross-site scripting vulnerability in hedgedoc, published on 30 Aug 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-2021-39175 in the wild and no public exploit code.

Affected product: hedgedoc. 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-2021-39175/ (Markdown: https://insights.sbomify.com/CVE-2021-39175/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-39175
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-39175
- OSV: https://osv.dev/vulnerability/CVE-2021-39175

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-39175/
Summaries are generated and may contain mistakes; the official description above is the record.