# CVE-2021-43817: Reflected Cross-Site-Scripting vulnerability in Collabora Online

> Attackers can inject scripts into Collabora Online iframes to steal user settings and session authentication tokens.

- **Severity:** High 8.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/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:** 13 Dec 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-7f6h-v9mx-58q9

## What is CVE-2021-43817?

CVE-2021-43817 is a high-severity cross-site scripting vulnerability in CollaboraOnline online, published on 13 Dec 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

Collabora Online is a collaborative online office suite based on LibreOffice technology. In affected versions a reflected XSS vulnerability was found in Collabora Online. An attacker could inject unescaped HTML into a variable as they created the Collabora Online iframe, and execute scripts inside the context of the Collabora Online iframe. This would give access to a small set of user settings stored in the browser, as well as the session's authentication token which was also passed in at iframe creation time. Users should upgrade to Collabora Online 6.4.16 or higher or Collabora Online 4.2.20 or higher. Collabora Online Development Edition 21.11 is not affected.

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

## Which versions are affected by CVE-2021-43817?

It affects 1 product.


Products: Collabora Online.

## How do I fix CVE-2021-43817?

No fix has been published for CVE-2021-43817 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-43817 being exploited?

There is no known exploitation of CVE-2021-43817 in the wild and no public exploit code.

## Other vulnerabilities in CollaboraOnline online

- [CVE-2026-110447](https://insights.sbomify.com/CVE-2026-110447/): Collabora Online – Built-in CODE Server OS Command Injection (critical 9.2, exploited in the wild)
- [CVE-2021-32744](https://insights.sbomify.com/CVE-2021-32744/): Unauthenticated attacker could gain access to currently open files (critical 9.8)
- [CVE-2021-32745](https://insights.sbomify.com/CVE-2021-32745/): Reflected Cross-Site-Scripting vulnerability (high 7.3)
- [CVE-2025-66208](https://insights.sbomify.com/CVE-2025-66208/): Configuration-Dependent RCE (OS Command Injection) in richdocumentscode proxy (high 7.2)
- [CVE-2024-45045](https://insights.sbomify.com/CVE-2024-45045/): JavaScript Injection via url encoded values in links in Collabora Office Android (medium 6.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-43817 and fix it if it is affected.

What it is: CVE-2021-43817 is a high-severity cross-site scripting vulnerability in CollaboraOnline online, published on 13 Dec 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-2021-43817 in the wild and no public exploit code.

Affected product: CollaboraOnline online. 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-2021-43817/ (Markdown: https://insights.sbomify.com/CVE-2021-43817/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-43817
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-43817
- OSV: https://osv.dev/vulnerability/CVE-2021-43817

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-43817/
Summaries are generated and may contain mistakes; the official description above is the record.