# CVE-2026-35390: Bulwark Webmail Cross-Site Scripting via CSP Misconfiguration

Source: https://junglewise.ai/threats/cve-2026-35390-bulwark-webmail-cross-site-scripting-via-csp-misconfiguration  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-06. Updated: 2026-07-24  
License: CC BY 4.0 with a link back

CVE-2026-35390 · Severity: medium · CVSS 5.4 · Published 2026-04-06

Bulwark Webmail is a self-hosted email client. A security flaw in its built-in proxy allowed malicious scripts in emails to run in a user's browser because security protections were set to 'report-only' mode instead of being enforced. This could allow an attacker to steal login sessions or perform unauthorized actions on behalf of a user who opens a malicious email.

## Quick answers

**Is CVE-2026-35390 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-35390 being exploited in the wild.

**How severe is CVE-2026-35390?** Medium severity, with a CVSS score of 5.4, published 6 April 2026.

**Which products and versions are affected?** Bulwark Webmail < 1.4.11.

**Is there a fix for CVE-2026-35390?** A patch was published on 2026-04-06: Fix released in version 1.4.11 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-35390 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-35390?** Check whether anything you run is named in the advisory. 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.

## Technical details

A vulnerability exists in Bulwark Webmail's reverse proxy (proxy.ts) where the Content-Security-Policy-Report-Only header was used instead of the enforcing Content-Security-Policy header. This misconfiguration effectively disabled CSP protections, allowing Cross-Site Scripting (XSS) attacks to proceed unblocked. An attacker can exploit this by sending a crafted HTML email containing malicious scripts. If a user views the email, the script executes in the context of the webmail application, enabling session token theft or unauthorized state-changing actions. The issue is resolved in version 1.4.11 by switching to an enforcing CSP header.

## Affected products

- Bulwark Webmail < 1.4.11

## Timeline

- 2026-04-02: advisory: GitHub Security Advisory published
- 2026-04-06: disclosed: CVE published to NVD
- 2026-04-06: patched: Fix released in version 1.4.11

## References

- [https://github.com/bulwarkmail/webmail/security/advisories/GHSA-6q52-98cr-qx65](https://github.com/bulwarkmail/webmail/security/advisories/GHSA-6q52-98cr-qx65)