CVE-2020-15139highCWE-79

CVE-2020-15139: high-severity vulnerability in MyBB

XSS in MyBB

Published · Updated

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21Vexday Risk Score

No sign of exploitation. No public exploitation artifact known so far.

ssvc Trackcvss 8.8epss 1.3%
In short

MyBB's visual editor fails to properly escape custom BBCode formatting, allowing attackers to inject malicious scripts that execute in a user's browser when viewing or editing messages. This can lead to account compromise or data theft.

Technical detail

DOM-based XSS vulnerability in MyBB's visual editor BBCode rendering mechanism (CWE-79). Attack vector involves crafting malicious MyCode messages delivered via GET/POST parameters or quoted replies; pre-condition requires victim to visit a page with the visual editor active. Impact includes arbitrary JavaScript execution in victim's browser context, potentially enabling session hijacking or credential theft.

Summary generated and translated by AI from the official description.
In MyBB before version 1.8.24, the custom MyCode (BBCode) for the visual editor doesn't escape input properly when rendering HTML, resulting in a DOM-based XSS vulnerability. The 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. After upgrading MyBB to 1.8.24, make sure to update the version attribute in the `codebuttons` template for non-default themes to serve the latest version of the patched `jscripts/bbcodes_sceditor.js` file.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Affected products
MyBB · MyBB