An issue was discovered in Django 2.0 before 2.0.3, 1.11 before 1.11.11, and 1.8 before 1.8.19. If django.utils.text.Truncator's chars() and words() methods were passed the html=True argument, they were extremely slow to evaluate certain inputs due to a catastrophic backtracking vulnerability in a regular expression. The chars() and words() methods are used to implement the truncatechars_html and truncatewords_html template filters, which were thus vulnerable.
https://www.djangoproject.com/weblog/2018/mar/06/security-releases/
https://www.debian.org/security/2018/dsa-4161
https://usn.ubuntu.com/3591-1/
https://lists.debian.org/debian-lts-announce/2018/03/msg00006.html
https://access.redhat.com/errata/RHSA-2019:0265