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.
- 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
- None listed
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
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.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-54521 being exploited?
There is no known exploitation of CVE-2026-54521 in the wild and no public exploit code.
Sources
Also known as GHSA-r8ff-qr7g-pvw6.