# CVE-2026-84371: ApostropheCMS: Stored XSS via SVG SMIL URI-list scheme-policy bypass

> Stored XSS in ApostropheCMS allows script execution via SVG SMIL attributes when animation elements are enabled.

- **Severity:** Medium 5.4 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 1 Sep 2026
- **Updated:** 2 Sep 2026
- **Also known as:** CLEANSTART-2026-LG36939, CLSA-2026-1788517172, ECHO-bd72-1c82-327f, GHSA-g8qq-57p8-ggw5, MINI-2jf4-jpmp-2ph2, MINI-555r-9x7w-9g7q, MINI-hm7c-hwmg-h75f, MINI-jf9v-mq99-xp4c

## What is CVE-2026-84371?

CVE-2026-84371 is a medium-severity cross-site scripting vulnerability in apostrophecms apostrophe, published on 1 Sep 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

ApostropheCMS is an open-source Node.js content management system, and sanitize-html provides a simple HTML sanitizer with a clear API. From version 1.9.0 until version 2.17.7, packages/sanitize-html/index.js validates an animation value attribute as one flat URL and does not recognize that attributeName selecting href or xlink:href gives the sibling values, from, to, or by attribute SVG SMIL URL semantics. In configurations that allow the animate, animateColor, animateMotion, animateTransform, or set elements, a values list can begin with a safe fragment and contain a later executable destination that survives allowedSchemesAppliedToAttributes checking. When the sanitized SVG is rendered, the browser can copy that later destination into the live link, and a victim who activates the link can execute script in the application's origin. This issue is fixed in version 2.17.7.

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

## Which versions are affected by CVE-2026-84371?

2 open source packages ship an affected version, including sanitize-html.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `sanitize-html` | npm | From 1.9.0 | 2.17.7 |
| `sanitize-html` | npm | From 1.9.0 | 2.17.7 |

## How do I fix CVE-2026-84371?

Upgrade sanitize-html to 2.17.7 or later.

## Is CVE-2026-84371 being exploited?

There is no known exploitation of CVE-2026-84371 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-84371 and fix it if it is affected.

What it is: CVE-2026-84371 is a medium-severity cross-site scripting vulnerability in apostrophecms apostrophe, published on 1 Sep 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-84371 in the wild and no public exploit code.

Affected packages and fixed versions:
- sanitize-html (npm): affected from 1.9.0; fixed in 2.17.7
- sanitize-html (npm): affected from 1.9.0; fixed in 2.17.7

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-2026-84371/ (Markdown: https://insights.sbomify.com/CVE-2026-84371/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-84371
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-84371
- OSV: https://osv.dev/vulnerability/CVE-2026-84371

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-84371/
Summaries are generated and may contain mistakes; the official description above is the record.