python before versions 2.7.15, 3.4.9, 3.5.6rc1, 3.6.5rc1 and 3.7.0 is vulnerable to catastrophic backtracking in pop3lib's apop() method. An attacker could use this flaw to cause denial of service.
https://www.oracle.com/security-alerts/cpujan2020.html
https://www.debian.org/security/2018/dsa-4307
https://www.debian.org/security/2018/dsa-4306
https://usn.ubuntu.com/3817-2/
https://usn.ubuntu.com/3817-1/
https://support.hpe.com/hpsc/doc/public/display?docLocale=en_US&docId=emr_na-hpesbst03951en_us
https://lists.debian.org/debian-lts-announce/2018/09/msg00031.html
https://lists.debian.org/debian-lts-announce/2018/09/msg00030.html
https://docs.python.org/3.6/whatsnew/changelog.html#python-3-6-5-release-candidate-1
https://docs.python.org/3.5/whatsnew/changelog.html#python-3-5-6-release-candidate-1
https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2018-1060
https://bugs.python.org/issue32981
https://access.redhat.com/errata/RHSA-2019:3725
https://access.redhat.com/errata/RHSA-2019:1260
https://access.redhat.com/errata/RHSA-2018:3505
https://access.redhat.com/errata/RHSA-2018:3041
https://access.redhat.com/errata/RHBA-2019:0327
http://www.securitytracker.com/id/1042001
http://lists.opensuse.org/opensuse-security-announce/2020-01/msg00040.html