Is CVE-2021-3737 in the CISA KEV catalog?

No. CVE-2021-3737 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2021-3737?

CVE-2021-3737 has a CVSS v3 base score of 7.5 (HIGH).

What is the EPSS score for CVE-2021-3737?

CVE-2021-3737 has an EPSS score of 11.99% (96th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2021-3737?

Upgrade pypy3 on debian 11 to 7.3.5+dfsg-2+deb11u4 or later. Fixes are available for 29 affected products.

CVE & CISA-KEV Catalog

CVE-2021-3737

HIGHEPSS 96th pctl

7.5

CVSS v3

NVD

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

pypy3Debian

Fixed in:7.3.5+dfsg-2+deb11u4CVE-2021-3737

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

libpython3.6-stdlibUbuntu

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

libpython3.7-stdlibUbuntu

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

libpython3.8-stdlibUbuntu

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

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

libpython3.9-stdlibUbuntu

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

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

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

python3.12Ubuntu

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

python3.12-minimalUbuntu

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

python3.4Ubuntu

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

python3.4-minimalUbuntu

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

python3.5Ubuntu

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

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

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

python3.5-minimalUbuntu

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

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

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

python3.6Ubuntu

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

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

python3.6-minimalUbuntu

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

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

python3.7Ubuntu

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

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

python3.7-minimalUbuntu

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

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

python3.8Ubuntu

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

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

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

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

python3.8-minimalUbuntu

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

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

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

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

python3.9Ubuntu

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

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

python3.9-minimalUbuntu

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

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

Python 2Windows application

Affected:3.9.0 3.9.6Fixed in:3.9.6Python Software Foundation

Affected:3.8.0 3.8.11Fixed in:3.8.11Python Software Foundation

Affected:3.7.0 3.7.11Fixed in:3.7.11Python Software Foundation

Affected:3.6.0 3.6.14Fixed in:3.6.14Python Software Foundation

Python 3.10Windows application

Affected:3.6.0 3.6.14Fixed in:3.6.14Python Software Foundation

Affected:3.8.0 3.8.11Fixed in:3.8.11Python Software Foundation

Affected:3.9.0 3.9.6Fixed in:3.9.6Python Software Foundation

Affected:3.7.0 3.7.11Fixed in:3.7.11Python Software Foundation

Python 3.11Windows application

Affected:3.6.0 3.6.14Fixed in:3.6.14Python Software Foundation

Affected:3.8.0 3.8.11Fixed in:3.8.11Python Software Foundation

Affected:3.9.0 3.9.6Fixed in:3.9.6Python Software Foundation

Affected:3.7.0 3.7.11Fixed in:3.7.11Python Software Foundation

Python 3.12Windows application

Affected:3.7.0 3.7.11Fixed in:3.7.11Python Software Foundation

Affected:3.9.0 3.9.6Fixed in:3.9.6Python Software Foundation

Affected:3.6.0 3.6.14Fixed in:3.6.14Python Software Foundation

Affected:3.8.0 3.8.11Fixed in:3.8.11Python Software Foundation

Python 3.8Windows application

Affected:3.9.0 3.9.6Fixed in:3.9.6Python Software Foundation

Affected:3.7.0 3.7.11Fixed in:3.7.11Python Software Foundation

Affected:3.8.0 3.8.11Fixed in:3.8.11Python Software Foundation

Affected:3.6.0 3.6.14Fixed in:3.6.14Python Software Foundation

Python 3.9Windows application

Affected:3.8.0 3.8.11Fixed in:3.8.11Python Software Foundation

Affected:3.7.0 3.7.11Fixed in:3.7.11Python Software Foundation

Affected:3.9.0 3.9.6Fixed in:3.9.6Python Software Foundation

Affected:3.6.0 3.6.14Fixed in:3.6.14Python Software Foundation

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

11.99%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	88%	-	Fix
CVE-2020-36227	High	7.5	78%	-	Fix
CVE-2024-20353	High	8.6	71%	KEV	-
CVE-2022-0778	High	7.5	71%	-	Fix
CVE-2019-14241	High	7.5	70%	-	-
CVE-2017-16944	High	7.5	63%	-	Fix

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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 2025-12-17.