The table extension in GitHub Flavored Markdown before version 0.29.0.gfm.1 takes O(n * n) time to parse certain inputs. An attacker could craft a markdown table which would take an unreasonably long time to process, causing a denial of service. This issue does not affect the upstream cmark project.
Created ghc-cmark-gfm tracking bugs for this issue:
Affects: fedora-all [bug 1854329]