We take the security of Wagtail, and related packages we maintain, seriously. If you have found a security issue with any of our projects please email us at security@wagtail.org so we can work together to find and patch the issue. We appreciate responsible disclosure with any security related issues, so please contact us first before creating a Github issue.
If you want to send an encrypted email (optional), the public key ID for security@wagtail.org is 0xbed227b4daf93ff9, and this public key is available from most commonly-used keyservers.