The smtplib library in CPython (aka Python) before 2.7.12, 3.x...

Vulnerability Description

The smtplib library in CPython (aka Python) before 2.7.12, 3.x before 3.4.5, and 3.5.x before 3.5.2 does not return an error when StartTLS fails, which might allow man-in-the-middle attackers to bypass the TLS protections by leveraging a network position between the client and the registry to block the StartTLS command, aka a "StartTLS stripping attack."

References

• https://hg.python.org/cpython/rev/d590114c2394
• http://www.splunk.com/view/SP-CAAAPUE
• http://rhn.redhat.com/errata/RHSA-2016-1630.html
• http://rhn.redhat.com/errata/RHSA-2016-1627.html
• https://hg.python.org/cpython/rev/b3ce713fb9be
• http://rhn.redhat.com/errata/RHSA-2016-1629.html
• http://www.splunk.com/view/SP-CAAAPSV
• https://lists.debian.org/debian-lts-announce/2019/02/msg00011.html
• https://bugzilla.redhat.com/show_bug.cgi?id=1303647
• https://docs.python.org/3.4/whatsnew/changelog.html#python-3-4-5
• http://www.openwall.com/lists/oss-security/2016/06/14/9
• https://hg.python.org/cpython/raw-file/v2.7.12/Misc/NEWS
• https://security.gentoo.org/glsa/201701-18
• https://docs.python.org/3.5/whatsnew/changelog.html#python-3-5-2
• http://www.securityfocus.com/bid/91225
• http://rhn.redhat.com/errata/RHSA-2016-1628.html
• http://rhn.redhat.com/errata/RHSA-2016-1626.html
• http://lists.opensuse.org/opensuse-security-announce/2020-01/msg00040.html