CVE-2020-15135: 
JavaScript vulnerability analysis and mitigation

A CSRF (Cross-Site Request Forgery) vulnerability was discovered in save-server (npm package) versions before 1.05, identified as CVE-2020-15135. The vulnerability stems from the absence of CSRF mitigation mechanisms such as tokens. While version 1.05 introduced a fix, it inadvertently broke the upload functionality, making version 1.0.7 the first fully patched version (GitHub Advisory).

The vulnerability exists due to the lack of CSRF protection mechanisms in the application. The issue specifically relates to missing token validation, which should prevent unauthorized cross-site requests. The fix implemented in version 1.0.7 uses the Double Submit Cookie Pattern, where a random value is sent in both a cookie and as a request parameter, with the server verifying if the cookie value and request value are equal (CSRF Pattern).

The vulnerability allows an attacker to perform unauthorized actions if a user with an active session visits a malicious website. For regular users, the attacker could upload files, delete files, and add redirects. For root users, the impact is more severe, allowing attackers to create users, delete users, and update user passwords. If an attacker updates a user's password, they could gain access to that user's files. If the root password is updated, all files would become accessible to the attacker (GitHub Advisory).

The CSRF attack requires the victim to have an active session with Save-Server (session key stored in cookies) while visiting a malicious website. Due to same-origin policy restrictions, attackers cannot view the gallery or the response of any methods, nor confirm if their attacks succeeded (GitHub Advisory).

Users should upgrade to version 1.0.7 or later, which implements the Double Submit Cookie Pattern as a CSRF mitigation measure. There are no alternative workarounds available; upgrading is the only recommended solution (GitHub Advisory).