The backtrack compilation code in the Irregex package (aka IrRegular Expressions) before 0.9.6 for Scheme allows remote attackers to cause a denial of service (memory consumption) via a crafted regular expression with a repeating pattern.
https://github.com/ashinn/irregex/commit/a16ffc86eca15fca9e40607d41de3cea9cf868f1
https://bugzilla.redhat.com/show_bug.cgi?id=1413990