Reverse Tabnabbing in showdown
Versions of `showdown` prior to 1.9.1 are vulnerable to Reverse Tabnabbing
https://www.owasp.org/index.php/Reverse_Tabnabbing. The package uses `target='_blank'` in anchor tags, allowing attackers to access `window.opener` for the original page when opening links. This is commonly used for phishing attacks.
## Recommendation
Upgrade to version 1.9.1 or later.