Summary

Attackers with access to a users’ device can gain persistent account access.
This is caused by missing verification of Session Tokens after password changes and/or elapsed inactivity-periods.

Details

uptime-kuma sets JWT tokens for users after successful authentication.

These tokens have the following design flaws:

• After successful login, a JWT token and it is stored in sessionStorage or localStorage.
  Which of the two is decided based on the Remember Me button.
  The users’ token is valid without any time limitation, even after long periods of inactivity.
  This increases the risk of session hijacking if, for example, a user forgets to log off and leaves the PC.
• sessions are only deleted on the client side after a user loggs out, meaning a local attacker could reuse said token with deep system access over the browser
• If a user changes a password
  • any previously logged in clients are not logged out
  • previously issued tokens remained valid forever

These flaws allow user cookies to remain valid even after changing passwords or being inactive, posing a high security risk.

POC

Password resets not deactivating cookies

• Log in.
• Note the user cookie.
• Change your password.
• Attempt to log in again with the same cookie.
• The cookie remains valid despite the password change.

Inactivity not deactivating sessions

In testing, even after a period of over a day of inactivity, the session was still valid

Impact

Another person with local access to the device could take over the session permanently, even after hours of previous inactivity or a password change.
Such activity would not be obvious to the user (see https://github.com/louislam/uptime-kuma/issues/3481 if you want to help with this).

With this gained account access, an attacker can cause:

confidentially loss

• monitors (including private ones not shared on public status pages)
• notification providers
• settings like api-keys (only used for accessing /metrics)
• settings like secrets like the Steam API Key
• maintenance periods

availability loss

• by creating a lot of monitors and setting the retention policy very high leading to degraded database performance or out of storage
• by creating a lot of HTTP(s) - Browser Engine (Chrome/Chromium) (Beta) leading to RAM exhaustion

integrity loss

• by the attacker deleting a monitor
• by the attacker deleting a monitor’s history
• by the atacker changing the meaning of a monitor (changing where it points)

scope creep

If operated in some restricted network, access to monitors may provide the ability to change the scope of the attack to a different piece of infrastructure, for example via SQL commands to a database server.
We have not classified this as changed scope because credentials stored in the application for accessing other systems are existing valid paths across the trust boundary, and the user should be aware of that.