In his Poetics, Aristotle does not write of a "tragic flaw" per se. Instead, rather than attributing the misfortunes of the hero to character flaws, the tragic fall is the result of hamartia,
a criminal act committed in ignorance of some material fact or even for the sake of a greater good.
Nevertheless, this act of injustice is often precipitated by the tragic hero's pride or other excessive emotion. In the case of Oedipus Rex, while hamartia constitutes his criminal act of murdering his own father and marrying his mother, it is his pride that keeps him ignorant of his being the cause of the plague under which Thebes suffers. For, he refuses to believe the seer Teiresias who first suggests--"But I say that you, with both your eyes, are blind"--and then bluntly states that Oedipus is the cause of the plague:
The man you have been looking for all this time,
The damned man, the murderer of Laios,
That man is in Thebes....
A revelation that will fail to please.
A blind man,
Who has his eyes now; a penniless man, who is rich now;....
To the children with whom he lives now he will be
Brother and father--the very same; to her
Who bore him, son and husband--the very same....
Who came to his father's bed, wet with his father's blood(434-445)
Certainly, then, the image of blood and the metaphor of blindness are used in the seer's message. These are repeated when, confronted with the horrific truth of his crime, Oedipus blinds himself with the brooches which Jocasta wears in her own death. He lifts them and puts out his eyes so that they
...would not see either the evils
he had suffered or the evils he had done,....
now only in darkness could they see those whom
they must not see, in darkness could they mistake
those whom they wanted to recognize.
Further, in his wish for oblivion, Oedipus includes another sensory image, as well, in order to ensure that he can escape a world of pain:
No, if I could just block off my ears, the springs of hearing, I would stop at nothing--
...not just the sight.
Oblivion--what a blessing...
Also, Oedipus thinks, "For why must I see/I for whom no sight is sweet." His "seeing" is both real and metaphoric: Oedipus Rex has been closed to the truth in his excessive pride, and the consequences of his realization are tragic. In the end, however, a new "sight" emerges in Oedipus with his newly acquired self-knowledge and newly-formed consciousness, so, ironically, he is not as blind as he was before he has lost his physical sense of sight.
But how does it answer the question:
Based upon the characterization made by Sophocles, if the reader must assign a "tragic flaw" to Oedipus, it would be his hubris, or excessive pride, that blinds him to the truth of the words of Teiresius.
The question asks what are tragic flaws according to Sophocles not as per Aristotle. So what constitutes tragic flaws according to Sophocles?
Here is a quotation from a college text, Perrine's Literature: Structure, Sound, & Sense:
The first great theorist of dramatic art was Aristotle (384-322 B.C.), whose discussion of tragedy in Poetics has dominated critical though ever since. A very brief summary of Aristotle's view will be helpful. [Then the play by Sophocles follows.]
Since Sophocles (496-406 B.C.) died before Aristotle was born (384-322 B.C.), and Aristotle was the first to define the elements of tragedy, we must assume that Sophocles did not define "tragic flaw" and can only rely on Aristotle's definition.
(A search for Sophocles's definition of tragic flaw will result in Aristotle's name and his work Poetics appearing)