CVE-2026-104083 SmarterMail < Build 9777 Stored Mutation XSS via MathML Foreign Content
Remote attackers can execute arbitrary scripts in victim webmail sessions via crafted iCal messages, enabling data exfiltration and session hijacking.
- 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-2026-104083?
CVE-2026-104083 is a medium-severity cross-site scripting vulnerability in Smartertools Smartermail, published on 9 Oct 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
SmarterMail before build 9777 contains a stored mutation cross-site scripting vulnerability that allows remote attackers to inject executable script by placing payloads inside a <style> element nested within MathML foreign content (<math><mtext><mglyph>), which the custom HTML sanitizer treats as inert CDATA text but browsers reparse as live markup. Attackers can deliver a crafted calendar (iCal) message containing an <img src=x onerror=...> payload that executes automatically in the recipient's webmail session at /interface/message-iframe when the message is opened, enabling script execution and data exfiltration unconstrained by the interface's permissive Content-Security-Policy.
Weakness: CWE-79
Which versions are affected by CVE-2026-104083?
How do I fix CVE-2026-104083?
No fix has been published for CVE-2026-104083 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-2026-104083 being exploited?
There is no known exploitation of CVE-2026-104083 in the wild and no public exploit code.
Sources
Also known as GHSA-vvh8-jc22-6q2f.