CVE-2026-35390 Content-Security-Policy was set to Report-Only mode, failing to block XSS attacks

Medium 5.3 Published 6 Apr 2026 Updated 7 Apr 2026

Attackers can execute arbitrary JavaScript via crafted emails because the Content-Security-Policy was set to Report-Only mode, allowing session theft.

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-2026-35390?

CVE-2026-35390 is a medium-severity cross-site scripting vulnerability in bulwarkmail webmail, published on 6 Apr 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

Bulwark Webmail is a self-hosted webmail client for Stalwart Mail Server. Prior to 1.4.11, the reverse proxy (proxy.ts) set the Content-Security-Policy-Report-Only header instead of the enforcing Content-Security-Policy header. This means cross-site scripting (XSS) attacks were logged but not blocked. Any user who could inject script content (e.g., via crafted email HTML) could execute arbitrary JavaScript in the context of the application, potentially stealing session tokens or performing actions on behalf of the user. This vulnerability is fixed in 1.4.11.

Weakness: CWE-79

Which versions are affected by CVE-2026-35390?

It affects 1 product.

Products include Bulwarkmail Webmail.

How do I fix CVE-2026-35390?

No fix has been published for CVE-2026-35390 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-2026-35390 being exploited?

There is no known exploitation of CVE-2026-35390 in the wild and no public exploit code.

Sources

Also known as GHSA-6q52-98cr-qx65.