A vulnerability was found in MyBB 1.8.6 (Content Management System). It has been classified as problematic. This affects some unknown processing of the component Forum Post Handler. The manipulation with an unknown input leads to a cross site scripting vulnerability. CWE is classifying the issue as CWE-80. The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special characters such as "<", ">", and "&" that could be interpreted as web-scripting elements when they are sent to a downstream component that processes web pages. This is going to have an impact on integrity.

The weakness was released 11/10/2016 by Tim Coen with Curesec Research Team as MyBB 1.8.6: XSS as not defined mailinglist post (Full-Disclosure). The advisory is shared at seclists.org. The public release was coordinated with the project team. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. It demands that the victim is doing some kind of user interaction. Technical details are unknown but a public exploit is available. MITRE ATT&CK project uses the attack technique T1059.007 for this issue. The advisory points out:

An admin can allow HTML input for specific forums via the setting allowhtml. There are various filters in place which intend to make this safe, which may leave the admin with the impression that it is indeed safe. However, there are various possibilities to bypass these filters, mainly using HTML5 features.

A public exploit has been developed by Tim Coen and been published immediately after the advisory. The exploit is shared for download at seclists.org. It is declared as proof-of-concept. The vulnerability was handled as a non-public zero-day exploit for at least 279 days. During that time the estimated underground price was around $5k-$25k.

Upgrading to version 1.8.7 eliminates this vulnerability. The upgrade is hosted for download at resources.mybb.com. A possible mitigation has been published before and not just after the disclosure of the vulnerability.

Entries connected to this vulnerability are available at 93560, 93562, 93563 and 93564.

Productinfo

Type

• Content Management System

Name

• MyBB

Version

• 1.8.6

License

• open-source

CPE 2.3info

• 🔍

CPE 2.2info

• 🔍

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