HOMEVULNERABILITIESCVE-2021-3737
HIGH

CVE-2021-3737

CWE-835Published: March 4, 2022· Updated: Jun 17, 2026

7.5
CVSS v3.1

Official 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.

NVD Source

Technical Analysis

CVE-2021-3737 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in availability disruption (denial of service), with a CVSS base score of 7.5.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
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

Affected Vendors & Products

Canonical1 product(s)
ubuntu linux
Fedora1 product(s)
fedora
netapp5 product(s)
hcimanagement services for element softwarenetapp xcp smbontap select deploy administration utilityxcp nfs
Oracle3 product(s)
communications cloud native core binding support functioncommunications cloud native core network exposure functioncommunications cloud native core policy
Python1 product(s)
python
Red Hat6 product(s)
codeready linux buildercodeready linux builder for ibm z systemscodeready linux builder for power little endianenterprise linuxenterprise linux for ibm z systemsenterprise linux for power little endian
Source: NVD CPE · 24 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

PATCHhttps://bugzilla.redhat.com/show_bug.cgi?id=1995162
PATCHhttps://github.com/python/cpython/pull/25916
PATCHhttps://github.com/python/cpython/pull/26503
PATCHhttps://python-security.readthedocs.io/vuln/urllib-100-continue-loop.html
PATCHhttps://ubuntu.com/security/CVE-2021-3737
PATCHhttps://www.oracle.com/security-alerts/cpujul2022.html
PATCHhttps://bugzilla.redhat.com/show_bug.cgi?id=1995162
PATCHhttps://github.com/python/cpython/pull/25916
PATCHhttps://github.com/python/cpython/pull/26503
PATCHhttps://python-security.readthedocs.io/vuln/urllib-100-continue-loop.html
PATCHhttps://ubuntu.com/security/CVE-2021-3737
PATCHhttps://www.oracle.com/security-alerts/cpujul2022.html
ADVISORYhttps://bugs.python.org/issue44022
ADVISORYhttps://security.netapp.com/advisory/ntap-20220407-0009/
ADVISORYhttps://bugs.python.org/issue44022
ADVISORYhttps://security.netapp.com/advisory/ntap-20220407-0009/

All References (22)

→
https://bugs.python.org/issue44022Exploit · Issue Tracking · Vendor Advisory
→
https://bugzilla.redhat.com/show_bug.cgi?id=1995162Issue Tracking · Patch · Third Party Advisory
→
https://github.com/python/cpython/pull/25916Patch · Third Party Advisory
→
https://github.com/python/cpython/pull/26503Patch · Third Party Advisory
→
https://lists.debian.org/debian-lts-announce/2023/05/msg00024.html
→
https://lists.debian.org/debian-lts-announce/2023/06/msg00039.html
→
https://python-security.readthedocs.io/vuln/urllib-100-continue-loop.htmlPatch · Third Party Advisory
→
https://security.netapp.com/advisory/ntap-20220407-0009/Third Party Advisory
→
https://ubuntu.com/security/CVE-2021-3737Patch · Third Party Advisory
→
https://www.oracle.com/security-alerts/cpujul2022.htmlPatch · Third Party Advisory
→
https://bugs.python.org/issue44022Exploit · Issue Tracking · Vendor Advisory
→
https://bugzilla.redhat.com/show_bug.cgi?id=1995162Issue Tracking · Patch · Third Party Advisory
→
https://github.com/python/cpython/pull/25916Patch · Third Party Advisory
→
https://github.com/python/cpython/pull/26503Patch · Third Party Advisory
→
https://lists.debian.org/debian-lts-announce/2023/05/msg00024.html

Quick Facts

CVE IDCVE-2021-3737
CVSS Score7.5 / 10
SeverityHIGH
WeaknessCWE-835
CISA KEVNo
Affected6 vendor(s)
PublishedMar 4, 2022

Related CVEs (CWE-835)

CVE-2017-12990
9.8
CVE-2017-12995
9.8
CVE-2017-12997
9.8
CVE-2018-20784
9.8
CVE-2021-42143
9.1
CVE-2024-43366
9.1

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-3737 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWatch. CVE data is provided under the NVD usage policy.
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