In my eye, it looks to me that the stock has cast off where it matters. As a rule of thumb, that you can verify, the eye is over the comb 1/3 the way back leaving the rear two thirds to meet your shoulder pocket. The curve looks to bring it back to your shoulder pocket. If you watch people shoot they often place the butt a bit to the right of the shoulder pocket and this stock would put it in the pocket more easily. This may have been caused by internal pressure inside the wood, maybe over time or by a gunsmith who was trying to solve a fit problem for an unknown shooter. Is this from a gun you own? Or just an old stock you came across? I agree with SKB that it would be almost impossible to straighten it out.
By removing the finish, you may be able to soak the stock in water and put it out in the sun. I did this with many warped doors and it worked well. When I got the correct bend back it was moved inside and the shape would remain permanently. Not sure you would want to try that with a stock.
