Standards get revised. While the 2011 version is still current (as of early 2025, though revisions are underway), you may find legitimate copies of older drafts or summaries on eBay or AbeBooks for as little as $20-$40. Ensure the seller is reputable.
This report details the official status of the standard, the risks associated with illegal downloads, and legal alternatives for accessing the content. iso 27031 standard pdf free