Mutt 1.11.0 through 2.0.x before 2.0.7 (and NeoMutt 2019-10-25 through 2021-05-04) has a $imap_qresync issue in which imap/util.c has an out-of-bounds read in situations where an IMAP sequence set ends with a comma. NOTE: the $imap_qresync setting for QRESYNC is not enabled by default.
https://security.gentoo.org/glsa/202105-05
https://gitlab.com/muttmua/mutt/-/commit/7c4779ac24d2fb68a2a47b58c7904118f40965d5
https://github.com/neomutt/neomutt/commit/fa1db5785e5cfd9d3cd27b7571b9fe268d2ec2dc
http://lists.mutt.org/pipermail/mutt-announce/Week-of-Mon-20210503/000036.html