# CVE-2026-54521: FairEmail: Cross-site scripting (XSS) in AMP message rendering (ActivityAMP)

> Attackers can execute arbitrary JavaScript in FairEmail's AMP renderer to steal message data or display phishing overlays if the user enables the AMP toggle.

- **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:** No
- **Published:** 17 Sep 2026
- **Updated:** 18 Sep 2026
- **Also known as:** GHSA-r8ff-qr7g-pvw6

## What is CVE-2026-54521?

CVE-2026-54521 is a medium-severity cross-site scripting vulnerability in M66B FairEmail, published on 17 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

FairEmail is a fully featured, open source, privacy-friendly email app for Android. Prior to 1.2319, the ActivityAMP AMP message renderer in app/src/main/java/eu/faircode/email/ActivityAMP.java enables JavaScript in its WebView but incompletely sanitizes untrusted message HTML. For non-allowlisted hosts, script.removeAttr("src") leaves inline script elements in the document and does not reject event-handler attributes or javascript: URLs on other elements. A crafted AMP email can execute arbitrary JavaScript when a recipient opens the message and enables the AMP toggle. The script can read the message DOM, exfiltrate message data, and display phishing overlays within the message-body area. Exploitation requires the recipient to enable the AMP toggle, and practical exposure is reduced because AMP email is uncommon. This issue is fixed in version 1.2319.

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

## Which versions are affected by CVE-2026-54521?


## How do I fix CVE-2026-54521?

No fix has been published for CVE-2026-54521 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-54521 being exploited?

There is no known exploitation of CVE-2026-54521 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-54521 and fix it if it is affected.

What it is: CVE-2026-54521 is a medium-severity cross-site scripting vulnerability in M66B FairEmail, published on 17 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: There is no known exploitation of CVE-2026-54521 in the wild and no public exploit code.

Affected product: M66B FairEmail. 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-2026-54521/ (Markdown: https://insights.sbomify.com/CVE-2026-54521/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-54521
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-54521
- OSV: https://osv.dev/vulnerability/CVE-2026-54521

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-54521/
Summaries are generated and may contain mistakes; the official description above is the record.