ApiMain.php, line 373:

} catch ( Exception $e ) {

line 380:

if ( $wgLogExceptionBacktrace ) {
wfDebugLog( 'exception', $e->getLogMessage() . "\n" . $e->getTraceAsString() . "\n" );
} else {
wfDebugLog( 'exception', $e->getLogMessage() );
}

Since getLogMessage() is defined MWException, if Exception caught is not MWException (which is allowed by catch), we get a call to undefined method fatal.

Version: 1.21.x
Severity: normal