Whatever you do, don't use salt! The amount of salt it would take to stop the bleeding process in fabrics will damage a washing machine. Vinegar might stop the fabric from bleeding more but I don't think it will help if it has already bled onto another fabric. I agree with the gals who have already posted, get one of the products especially created to help with this problem.
Are you having a problem with a specific fabric? If so, I would say to toss that fabric and don't use it. Tear it into strips and reuse in the garden if you want, but take it far, far away from your quilting space so you don't accidentally use it in something else.
I'm a big fan of pre-washing fabrics. I keep meaning to try the dye catchers but so far I haven't managed to buy them. Instead I use a small piece of muslin to help me make sure none of my fabrics are going to run. I toss a 3-6 inch square in with the wash & check it once the wash is done. If there is dye, I rewash whatever fabric is leaking and see if that helps. I also toss a muslin sheet into the dryer with my fabric. If it picks up any dye, then I usually toss that fabric away from my quilting projects, or use it in the garden, or to make a practice block that isn't going to be used for anything. With the exception of a handful of fabrics over the years, prewashing has saved me a lot of time and trouble. I highly recommend it to those who don't but might be having trouble in this area.