# CVE-2026-40186: ApostropheCMS: sanitize-html allowedTags Bypass via Entity-Decoded Text in nonTextTags Elements

> Attackers can inject arbitrary HTML and scripts via entity-encoded text in textarea or option elements, bypassing sanitization filters in ApostropheCMS.

- **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:** 15 Apr 2026
- **Updated:** 16 Apr 2026
- **Also known as:** GHSA-9mrh-v2v3-xpfm

## What is CVE-2026-40186?

CVE-2026-40186 is a medium-severity cross-site scripting vulnerability in apostrophecms apostrophe, published on 15 Apr 2026. 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

ApostropheCMS is an open-source Node.js content management system. A regression introduced in commit 49d0bb7, included in versions 2.17.1 of the ApostropheCMS-maintained sanitize-html package bypasses allowedTags enforcement for text inside nonTextTagsArray elements (textarea and option). ApostropheCMS version 4.28.0 is affected through its dependency on the vulnerable sanitize-html version. The code at packages/sanitize-html/index.js:569-573 incorrectly assumes that htmlparser2 does not decode entities inside these elements and skips escaping, but htmlparser2 10.x does decode entities before passing text to the ontext callback. As a result, entity-encoded HTML is decoded by the parser and then written directly to the output as literal HTML characters, completely bypassing the allowedTags filter. An attacker can inject arbitrary tags including XSS payloads through any allowed option or textarea element using entity encoding. This affects non-default configurations where option or textarea are included in allowedTags, which is common in form builders and CMS platforms. This issue has been fixed in version 2.17.2 of sanitize-html and 4.29.0 of ApostropheCMS.

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

## Which versions are affected by CVE-2026-40186?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `sanitize-html` | npm | From 2.17.2 | 2.17.3 |
| `sanitize-html` | npm | From 2.17.2 | 2.17.3 |

Products: Apostrophecms Apostrophecms, Apostrophecms Sanitize-Html.

## How do I fix CVE-2026-40186?

Upgrade sanitize-html to 2.17.3 or later.

## Is CVE-2026-40186 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40186 exists.

## Other vulnerabilities in apostrophecms apostrophe

- [CVE-2021-25979](https://insights.sbomify.com/CVE-2021-25979/): Apostrophe - Insufficient Session Expiration (critical 9.8)
- [CVE-2026-35569](https://insights.sbomify.com/CVE-2026-35569/): ApostropheCMS: Stored XSS in SEO Fields Leads to Authenticated API Data Exposure in ApostropheCMS (high 8.7)
- [CVE-2026-32730](https://insights.sbomify.com/CVE-2026-32730/): ApostropheCMS MFA/TOTP Bypass via Incorrect MongoDB Query in Bearer Token Middleware (high 8.1)
- [CVE-2026-33889](https://insights.sbomify.com/CVE-2026-33889/): ApostropheCMS: Stored XSS via CSS Custom Property Injection in `@apostrophecms/color-field` Escaping Style Tag Context (medium 5.4)
- [CVE-2021-25978](https://insights.sbomify.com/CVE-2021-25978/): Apostrophe - XSS (medium 5.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40186 and fix it if it is affected.

What it is: CVE-2026-40186 is a medium-severity cross-site scripting vulnerability in apostrophecms apostrophe, published on 15 Apr 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40186 exists.

Affected packages and fixed versions:
- sanitize-html (npm): affected from 2.17.2; fixed in 2.17.3
- sanitize-html (npm): affected from 2.17.2; fixed in 2.17.3

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-2026-40186/ (Markdown: https://insights.sbomify.com/CVE-2026-40186/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40186
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40186
- OSV: https://osv.dev/vulnerability/CVE-2026-40186

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40186/
Summaries are generated and may contain mistakes; the official description above is the record.