1Panel – CAPTCHA Bypass via Client-Controlled Flag

Summary

A CAPTCHA bypass vulnerability in the 1Panel authentication API allows an unauthenticated attacker to disable CAPTCHA verification by abusing a client-controlled parameter. Because the server previously trusted this value without proper validation, CAPTCHA protections could be bypassed, enabling automated login attempts and significantly increasing the risk of account takeover (ATO).

Details

The /api/login endpoint accepts a boolean field named ignoreCaptcha directly from the client request body:

"ignoreCaptcha": true

The backend implementation uses this value to determine whether CAPTCHA validation should be performed:

if !req.IgnoreCaptcha {
    if errMsg := captcha.VerifyCode(req.CaptchaID, req.Captcha); errMsg != "" {
        helper.BadAuth(c, errMsg, nil)
        return
    }
}

Because req.IgnoreCaptcha is taken directly from user input—with no server-side validation, no session binding, and no privilege checks—any unauthenticated attacker can force CAPTCHA validation to be skipped.

There are no additional conditions, such as:

no requirement for MFA

no trusted device

no IP reputation checks

no prior valid session

no rate limiting

This results in CAPTCHA being entirely client-controlled, which violates fundamental authentication and anti-automation security assumptions.