Quick answers
- Is CVE-2026-104083 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-104083 being exploited in the wild.
- How severe is CVE-2026-104083?
- Medium severity, with a CVSS score of 6.1, published 9 October 2026.
- Which products and versions are affected?
- SmarterTools SmarterMail before build 9777.
- Is there a fix for CVE-2026-104083?
- Yes: fixed in SmarterMail build 9777. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-104083 attacked?
- It is attacked over the network, in a web application.
- Am I affected by CVE-2026-104083?
- Check whether you run SmarterTools SmarterMail at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
How to fix
- Fixed in: SmarterMail build 9777
Technical details
The vulnerability is a mutation XSS arising from a parser differential between SmarterMail's custom HTML sanitizer (which treats <style> tags as CDATA text) and browser parsing of foreign content (MathML/SVG). An attacker can craft a message with nested MathML containing <style><img src=x onerror=...></style>, which the sanitizer passes through but browsers reparse as executable markup. The attack requires only that a recipient opens the message in /interface/message-iframe; SmarterMail's permissive CSP (script-src *, unsafe-inline) does not constrain the injected script.
Affected products
- SmarterTools SmarterMail before build 9777
Timeline
- 2026-10-09: disclosed