MyBB Theme Import Stylesheet Name Remote Code Execution Vulnerability

CVE-2019-12831 · MEDIUM Severity

AV:N/AC:L/AU:S/C:P/I:P/A:P

In MyBB before 1.8.21, an attacker can abuse a default behavior of MySQL on many systems (that leads to truncation of strings that are too long for a database column) to create a PHP shell in the cache directory of a targeted forum via a crafted XML import, as demonstrated by truncation of aaaaaaaaaaaaaaaaaaaaaaaaaa.php.css to aaaaaaaaaaaaaaaaaaaaaaaaaa.php with a 30-character limit, aka theme import stylesheet name RCE.

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