You will have to for give me for taking a slight detour before actually telling you what the source of evil is.

Let us consider for a moment what it would mean if "Evil" was capable of being "objectified" whether it appears as a yellow watermelon or as the mythographic "Lucifer" or "Satan"... If one were to accept that way of thinking then they are accepting that there is more than one thing with "god-like" powers. Dualism [as it is called] assumes that there is a thing of "ultimate good" and a thing of "ultimate evil"-- but that is not monotheism which allegedly is the foundation of most of the "Abrahamic" religions.

"Satan" is a Christian abbreviation of a Hebrew "title" given to one of the Hebrew God's angels, "Ha Satan" which litterally means "The Accuser". It is his "job" to accuse "sinners" before the "Throne of Glory" that the sinners can not get away "unpunished". You might think of this Malach [Hebrew for 'messenger' or "angel"] as the Special Prosecutor of Human Evil. As time went along and Christianity re-interpreted the Hebrew texts, "Satan" took on a godlike sheen all its own as adapted from the Manichean and the Zoroastrian theologies.. But that is not what Monotheism means. Monotheism has only one power that being the "Creator-God"... there is no room for another "power".

So by now I'm sure you're asking 'Where did 'evil' come from then? The answer to that is simple: humanity created 'evil' in all its forms [See that paragraph in Genesis about God gave man dominion over the world]. Think about it for a moment: who created that yellow hearted GMO spawn of the garden? Humans. Who picked it and smiled at the idea of the money to be made selling it? Humans. Who did you buy it from? A human. No objectified entity other than a human was responsible for a watermelon of a different color.

Finally we return to a 'human duality" taken from the Hebrew. Humans have the power / intention to create goodness -- "Yetzer Ha Tov" and the power / intention to create Evil -- "Yetzer Ha Ra". You might think back to those old cartoons where an "angel" sits on the right shoulder and a "demon" sits upon the left... Most of those cartoons were created by Jewish Artist / Animators. That is as near as Jewish thought gets in regards to evil. Neither objects nor demigods create evil. Evil is created by people... After all who created "Soylent Green"?

[an aside: The four seasons of California (and everywhere else), that is, Rain, Mud, Fire, and Earthquake are not 'evil' -- they are just random events which happen. There is no punishment or retribution implied by these events they are just a part of the way the world must work for it to function properly-- with the exception of you got it - human induced Climate Change.]