# CVE-2026-31833: Umbraco has Stored XSS in UFM Rendering Pipeline via Permissive DOMPurify Attribute Filtering

> Authenticated backoffice users can inject malicious HTML into property descriptions due to permissive DOMPurify filtering, leading to stored XSS.

- **Severity:** Medium 6.7 (`CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 10 Mar 2026
- **Updated:** 11 Mar 2026
- **Also known as:** GHSA-vrqc-59mw-qqg7

## What is CVE-2026-31833?

CVE-2026-31833 is a medium-severity cross-site scripting vulnerability in Umbraco Umbraco Cms, published on 10 Mar 2026. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

Umbraco is an ASP.NET CMS. From 16.2.0 to before 16.5.1 and 17.2.2, An authenticated backoffice user with access to Settings can inject malicious HTML into property type descriptions. Due to an overly permissive attributeNameCheck configuration (/.+/) in the UFM DOMPurify instance, event handler attributes such as onclick and onload, when used within Umbraco web components (umb-*, uui-*, ufm-*) were not filtered. This vulnerability is fixed in 16.5.1 and 17.2.2.

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

## Which versions are affected by CVE-2026-31833?

4 open source packages ship an affected version, including Umbraco.Cms. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `Umbraco.Cms` | NuGet | From 16.2.0 | 16.5.1 |
| `Umbraco.Cms` | NuGet | From 16.2.0 | 16.5.1 |
| `Umbraco.Cms` | NuGet | From 17.0.0 | 17.2.2 |
| `Umbraco.Cms` | NuGet | From 17.0.0 | 17.2.2 |

Products: Umbraco Umbraco Cms.

## How do I fix CVE-2026-31833?

Upgrade Umbraco.Cms to a fixed version for your release line: 16.5.1 or 17.2.2.

## Is CVE-2026-31833 being exploited?

There is no known exploitation of CVE-2026-31833 in the wild and no public exploit code.

## Other vulnerabilities in Umbraco Umbraco Cms

- [CVE-2025-67288](https://insights.sbomify.com/CVE-2025-67288/): Umbraco CMS has an arbitrary file upload vulnerability (critical 10.0)
- [CVE-2014-10074](https://insights.sbomify.com/CVE-2014-10074/): File upload in n/a (critical 9.8)
- [CVE-2012-1301](https://insights.sbomify.com/CVE-2012-1301/): Server-side request forgery in n/a (critical 9.8)
- [CVE-2012-10054](https://insights.sbomify.com/CVE-2012-10054/): Umbraco CMS < 4.7.1 codeEditorSave.asmx RCE (critical 9.3)
- [CVE-2025-32017](https://insights.sbomify.com/CVE-2025-32017/): Umbraco has a Management API Vulnerability to Path Traversal With Authenticated Users (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-31833 and fix it if it is affected.

What it is: CVE-2026-31833 is a medium-severity cross-site scripting vulnerability in Umbraco Umbraco Cms, published on 10 Mar 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-31833 in the wild and no public exploit code.

Affected packages and fixed versions:
- Umbraco.Cms (NuGet): affected from 16.2.0; fixed in 16.5.1
- Umbraco.Cms (NuGet): affected from 16.2.0; fixed in 16.5.1
- Umbraco.Cms (NuGet): affected from 17.0.0; fixed in 17.2.2
- Umbraco.Cms (NuGet): affected from 17.0.0; fixed in 17.2.2

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-2026-31833/ (Markdown: https://insights.sbomify.com/CVE-2026-31833/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31833
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31833
- OSV: https://osv.dev/vulnerability/CVE-2026-31833

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31833/
Summaries are generated and may contain mistakes; the official description above is the record.