# CVE-2026-100370: Cross-site scripting in dom-sanitizer

> Attackers can bypass URL sanitization using Base64-encoded data URLs to inject malicious scripts, leading to cross-site scripting attacks.

- **Severity:** Medium 4.7 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/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:** 28 Sep 2026
- **Updated:** 28 Sep 2026
- **Also known as:** GHSA-wcj2-r6vg-rm97

## What is CVE-2026-100370?

CVE-2026-100370 is a medium-severity cross-site scripting vulnerability in rhukster dom-sanitizer, published on 28 Sep 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

DOMSanitizer is a DOM/SVG/MathML Sanitizer for PHP 7.3+. Prior to version 1.0.15, the isDangerousUrl() method is responsible for rejecting dangerous URL values in the href and xlink:href attributes. The weakness is that "javascript:" is rejected as a scheme, while "data:" is rejected only when the literal substring onload appears in the URL value (/^data:.*onload/i). Because data: payloads are routinely Base64-encoded, the dangerous content (<script>, event handlers, etc.) is invisible to that substring test. A URL such as data:text/html;base64,… therefore survives in href / xlink:href, even though the decoded payload is active markup. This is an incomplete input-validation / sanitization defect in the sanitizer itself. This issue has been patched in version 1.0.15.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2026-100370?


## How do I fix CVE-2026-100370?

No fix has been published for CVE-2026-100370 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-100370 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-100370 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-100370 and fix it if it is affected.

What it is: CVE-2026-100370 is a medium-severity cross-site scripting vulnerability in rhukster dom-sanitizer, published on 28 Sep 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-2026-100370 exists.

Affected product: rhukster dom-sanitizer. 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-2026-100370/ (Markdown: https://insights.sbomify.com/CVE-2026-100370/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-100370
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-100370
- OSV: https://osv.dev/vulnerability/CVE-2026-100370

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-100370/
Summaries are generated and may contain mistakes; the official description above is the record.