CVE-2021-3737

HIGHEPSS 96th pctl

7.5

CVSS v3

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.

CWE-835 CWE-400Resource Exhaustion

How to fix

Remediation Available

pythonAmazon

Fixed in:0:2.7.18-1.amzn2.0.5

python-debugAmazon

Fixed in:0:2.7.18-1.amzn2.0.5

python-debuginfoAmazon

Fixed in:0:2.7.18-1.amzn2.0.5

python-develAmazon

Fixed in:0:2.7.18-1.amzn2.0.5

python-libsAmazon

Fixed in:0:2.7.18-1.amzn2.0.5

python-testAmazon

Fixed in:0:2.7.18-1.amzn2.0.5

python-toolsAmazon

Fixed in:0:2.7.18-1.amzn2.0.5

tkinterAmazon

Fixed in:0:2.7.18-1.amzn2.0.5

pypy3Debian

Fixed in:7.3.8+dfsg-1CVE-2021-3737

libpython3.6-stdlibUbuntu

Fixed in:3.6.9-1~18.04ubuntu1.6USN-5199-1

This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.

libpython3.7-stdlibUbuntu

Fixed in:3.7.5-2ubuntu1~18.04.2USN-5200-1

This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.

libpython3.8-stdlibUbuntu

Fixed in:3.8.0-3ubuntu1~18.04.2USN-5200-1

This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.

Fixed in:3.8.10-0ubuntu1~20.04.2USN-5201-1

This Ubuntu release reached end-of-life on 2025-05-31. Extended security maintenance is available until 2030-04-02.

libpython3.9-stdlibUbuntu

Fixed in:3.9.5-3ubuntu0~20.04.1USN-5201-1

This Ubuntu release reached end-of-life on 2025-05-31. Extended security maintenance is available until 2030-04-02.

python3.10Ubuntu

Fixed in:3.10.12-1~22.04.4USN-6891-1

python3.10-minimalUbuntu

Fixed in:3.10.12-1~22.04.4USN-6891-1

python3.11Ubuntu

Fixed in:3.11.0~rc1-1~22.04.1~esm1USN-6891-1

Fixed in:3.11.6-3ubuntu0.1USN-6891-1

This Ubuntu release reached end-of-life on 2024-07-12.

python3.11-minimalUbuntu

Fixed in:3.11.0~rc1-1~22.04.1~esm1USN-6891-1

Fixed in:3.11.6-3ubuntu0.1USN-6891-1

This Ubuntu release reached end-of-life on 2024-07-12.

python3.12Ubuntu

Fixed in:3.12.0-1ubuntu0.1USN-6891-1

This Ubuntu release reached end-of-life on 2024-07-12.

python3.12-minimalUbuntu

Fixed in:3.12.0-1ubuntu0.1USN-6891-1

This Ubuntu release reached end-of-life on 2024-07-12.

python3.4Ubuntu

Fixed in:3.4.3-1ubuntu1~14.04.7+esm11USN-5083-1

This Ubuntu release reached end-of-life on 2019-04-02.

python3.4-minimalUbuntu

Fixed in:3.4.3-1ubuntu1~14.04.7+esm11USN-5083-1

This Ubuntu release reached end-of-life on 2019-04-02.

python3.5Ubuntu

Fixed in:3.5.2-2ubuntu0~16.04.4~14.04.1+esm1USN-6891-1

This Ubuntu release reached end-of-life on 2019-04-02.

Fixed in:3.5.2-2ubuntu0~16.04.13+esm13USN-6891-1

This Ubuntu release reached end-of-life on 2021-04-02.

Fixed in:3.5.2-2ubuntu0~16.04.13+esm1USN-5083-1

This Ubuntu release reached end-of-life on 2021-04-02.

python3.5-minimalUbuntu

Fixed in:3.5.2-2ubuntu0~16.04.4~14.04.1+esm1USN-6891-1

This Ubuntu release reached end-of-life on 2019-04-02.

Fixed in:3.5.2-2ubuntu0~16.04.13+esm13USN-6891-1

This Ubuntu release reached end-of-life on 2021-04-02.

Fixed in:3.5.2-2ubuntu0~16.04.13+esm1USN-5083-1

This Ubuntu release reached end-of-life on 2021-04-02.

python3.6Ubuntu

Fixed in:3.6.9-1~18.04ubuntu1.6USN-5199-1

This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.

Fixed in:3.6.9-1~18.04ubuntu1.13+esm2USN-6891-1

This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.

python3.6-minimalUbuntu

Fixed in:3.6.9-1~18.04ubuntu1.13+esm2USN-6891-1

This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.

Fixed in:3.6.9-1~18.04ubuntu1.6USN-5199-1

This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.

python3.7Ubuntu

Fixed in:3.7.5-2ubuntu1~18.04.2USN-5200-1

This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.

Fixed in:3.7.5-2ubuntu1~18.04.2+esm3USN-6891-1

This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.

python3.7-minimalUbuntu

Fixed in:3.7.5-2ubuntu1~18.04.2USN-5200-1

This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.

Fixed in:3.7.5-2ubuntu1~18.04.2+esm3USN-6891-1

This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.

python3.8Ubuntu

Fixed in:3.8.0-3ubuntu1~18.04.2+esm2USN-6891-1

This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.

Fixed in:3.8.0-3ubuntu1~18.04.2USN-5200-1

This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.

Fixed in:3.8.10-0ubuntu1~20.04.2USN-5201-1

This Ubuntu release reached end-of-life on 2025-05-31. Extended security maintenance is available until 2030-04-02.

Fixed in:3.8.10-0ubuntu1~20.04.10USN-6891-1

This Ubuntu release reached end-of-life on 2025-05-31. Extended security maintenance is available until 2030-04-02.

python3.8-minimalUbuntu

Fixed in:3.8.0-3ubuntu1~18.04.2USN-5200-1

This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.

Fixed in:3.8.0-3ubuntu1~18.04.2+esm2USN-6891-1

This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.

Fixed in:3.8.10-0ubuntu1~20.04.10USN-6891-1

This Ubuntu release reached end-of-life on 2025-05-31. Extended security maintenance is available until 2030-04-02.

Fixed in:3.8.10-0ubuntu1~20.04.2USN-5201-1

This Ubuntu release reached end-of-life on 2025-05-31. Extended security maintenance is available until 2030-04-02.

python3.9Ubuntu

Fixed in:3.9.5-3ubuntu0~20.04.1USN-5201-1

This Ubuntu release reached end-of-life on 2025-05-31. Extended security maintenance is available until 2030-04-02.

Fixed in:3.9.5-3ubuntu0~20.04.1+esm2USN-6891-1

This Ubuntu release reached end-of-life on 2025-05-31. Extended security maintenance is available until 2030-04-02.

This vulnerability affects an unusually large number of packages. The highest-confidence fixes are shown above; the full list is longer. Check the referenced advisories for complete coverage.

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Exploit Intelligence

11.59%probability of exploitation in 30 days

96thpercentile

Very high risk: more likely to be exploited than 96% of all known CVEs.

References

Patch6

Exploit1

bugs.python.org

Third-Party Advisory1

security.netapp.com

Other references4

Related Vulnerabilities

Other CWE-835 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2020-13935	High	7.5	87%	-	Fix
CVE-2020-36227	High	7.5	78%	-	Fix
CVE-2022-0778	High	7.5	73%	-	Fix
CVE-2024-20353	High	8.6	71%	KEV	-
CVE-2019-14241	High	7.5	70%	-	-
CVE-2017-16944	High	7.5	63%	-	Fix

Common questions

How do I fix CVE-2021-3737?

Published advisories record a fix for 37 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.

Is CVE-2021-3737 being actively exploited?

Not that we know of. CVE-2021-3737 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 11.6% is the estimated probability that it will be exploited in the next 30 days. That is higher than 96% of all scored CVEs.

How severe is CVE-2021-3737?

CVE-2021-3737 has a CVSS v3 base score of 7.5, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

What does CVE-2021-3737 affect?

Published advisories record a fix for python (Amazon), python-debug (Amazon), python-debuginfo (Amazon), python-devel (Amazon), and 33 more. Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

Embed a live status badge for CVE-2021-3737

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-06-17.