CVE-2023-46251
Visual editor persistent Cross-site Scripting (XSS) in MyBB
In short
MyBB's visual editor doesn't properly clean up malicious code in forum messages, allowing attackers to inject harmful scripts that execute in victims' browsers when they view or reply to specially crafted posts. This can lead to account hijacking, credential theft, or unauthorized actions on the forum.
Technical detail
DOM-based XSS vulnerability in MyBB's visual editor (_SCEditor_) where custom MyCode parsing fails to escape HTML entities during rendering. Attack vectors include pre-filled GET/POST parameters and quoted malicious messages; exploitation occurs when victims access pages with the visual editor enabled and interact with crafted MyCode content, potentially allowing session hijacking or malware injection.
Summary generated and translated by AI from the official description.
MyBB is a free and open source forum software. Custom MyCode (BBCode) for the visual editor (_SCEditor_) doesn't escape input properly when rendering HTML, resulting in a DOM-based XSS vulnerability. This weakness can be exploited by pointing a victim to a page where the visual editor is active (e.g. as a post or Private Message) and operates on a maliciously crafted MyCode message. This may occur on pages where message content is pre-filled using a GET/POST parameter, or on reply pages where a previously saved malicious message is quoted. The impact is be mitigated when: 1. the visual editor is disabled globally (_Admin CP → Configuration → Settings → Clickable Smilies and BB Code: [Clickable MyCode Editor](https://github.com/mybb/mybb/blob/mybb_1836/install/resources/settings.xml#L2087-L2094)_ is set to _Off_), or 2. the visual editor is disabled for individual user accounts (_User CP → Your Profile → Edit Options_: _Show the MyCode formatting options on the posting pages_ checkbox is not checked). MyBB 1.8.37 resolves this issue with the commit `6dcaf0b4d`. Users are advised to upgrade. Users unable to upgrade may mitigate the impact without upgrading MyBB by changing the following setting (_Admin CP → Configuration → Settings_):
- _Clickable Smilies and BB Code → [Clickable MyCode Editor](https://github.com/mybb/mybb/blob/mybb_1836/install/resources/settings.xml#L2087-L2094)_: _Off_. Similarly, individual MyBB forum users are able to disable the visual editor by diabling the account option (_User CP → Your Profile → Edit Options_) _Show the MyCode formatting options on the posting pages_.
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H