CVE-2021-3733: Medium severity Python Python vulnerability

Published Aug 10, 2021
·
Updated

Python is vulnerable to a denial of service, caused by a regular expression denial of service (ReDoS) flaw in the AbstractBasicAuthHandler class in urllib. By persuading a victim to visit a specially-crafted web site, a remote attacker could exploit this vulnerability to cause a denial of service condition.

Other sources

The ReDoS-vulnerable regex has quadratic worst-case complexity and it allows cause a denial of service when identifying crafted invalid RFCs. This ReDoS issue is on the client side and needs remote attackers to control the HTTP server.

References:

https://bugs.python.org/issue43075 https://github.com/python/cpython/pull/24391

— Red Hat

There's a flaw in urllib's AbstractBasicAuthHandler class. An attacker who controls a malicious HTTP server that an HTTP client (such as web browser) connects to, could trigger a Regular Expression Denial of Service (ReDOS) during an authentication request with a specially crafted payload that is sent by the server to the client. The greatest threat that this flaw poses is to application availability.

— Ubuntu

There's a flaw in urllib's AbstractBasicAuthHandler class. An attacker who controls a malicious HTTP server that an HTTP client (such as web browser) connects to could trigger a Regular Expression Denial of Service (ReDOS) during an authentication request with a specially crafted payload that is sent by the server to the client. The greatest threat that this flaw poses is to application availability.

— Microsoft

Affected Software

45 affected componentsFixes available
redhat/python3<0:3.6.8-39.el8_4
0:3.6.8-39.el8_4
redhat/rh-python38-babel<0:2.7.0-12.el7
0:2.7.0-12.el7
redhat/rh-python38-python<0:3.8.11-2.el7
0:3.8.11-2.el7
redhat/rh-python38-python-cryptography<0:2.8-5.el7
0:2.8-5.el7
redhat/rh-python38-python-jinja2<0:2.10.3-6.el7
0:2.10.3-6.el7
redhat/rh-python38-python-lxml<0:4.4.1-7.el7
0:4.4.1-7.el7
redhat/rh-python38-python-pip<0:19.3.1-2.el7
0:19.3.1-2.el7
redhat/rh-python38-python-urllib3<0:1.25.7-7.el7
0:1.25.7-7.el7
redhat/python27-python<0:2.7.18-4.el7
0:2.7.18-4.el7
Python Python<3.6.14
Python Python>=3.7.0<3.7.11
Python Python>=3.8.0<3.8.10
Python Python>=3.9.0<3.9.5
Python Python=3.10.0
redhat Codeready Linux Builder=8.0
redhat Codeready Linux Builder For Ibm Z Systems=8.0
redhat Codeready Linux Builder For Power Little Endian=8.0
redhat Enterprise Linux=8.0
redhat Enterprise Linux Eus=8.4
redhat Enterprise Linux For Ibm Z Systems=8.0
redhat Enterprise Linux For Ibm Z Systems Eus=8.4
redhat Enterprise Linux For Power Little Endian=8.0
redhat Enterprise Linux For Power Little Endian Eus=8.4
redhat Enterprise Linux Server Aus=8.4
redhat Enterprise Linux Server For Power Little Endian Update Services For Sap Solutions=8.4
redhat Enterprise Linux Server Tus=8.4
redhat Enterprise Linux Server Update Services For Sap Solutions=8.4
Fedoraproject Extra Packages For Enterprise Linux=7.0
Fedoraproject Fedora=33
Fedoraproject Fedora=34
Fedoraproject Fedora=35
Fedoraproject Fedora=36
NetApp Management Services For Element Software And Netapp Hci
NetApp ONTAP Select Deploy administration utility
NetApp Solidfire\, Enterprise Sds \& Hci Storage Node
NetApp Hci Compute Node Firmware
IBM Cognos Analytics 11.2.x<=IBM Cognos Analytics 11.2.x
IBM Cognos Analytics 11.1.x<=IBM Cognos Analytics 11.1.x
redhat/python<3.6.14
3.6.14
redhat/python<3.7.11
3.7.11
redhat/python<3.8.10
3.8.10
redhat/python<3.9.5
3.9.5
debian/pypy3
7.3.11+dfsg-2+deb12u37.3.19+dfsg-28.0.1+dfsg-1
All of the following
azurelinux/python2<2.7.18-10
2.7.18-10
Microsoft CBL-Mariner=1.0

Remediation

Recommended actions to resolve this vulnerability, in priority order.

  1. Upgrade

    Upgrade redhat/python3 to a version that resolves this vulnerability.

    Fixed in 0:3.6.8-39.el8_4
  2. Upgrade

    Upgrade redhat/rh-python38-babel to a version that resolves this vulnerability.

    Fixed in 0:2.7.0-12.el7
  3. Upgrade

    Upgrade redhat/rh-python38-python to a version that resolves this vulnerability.

    Fixed in 0:3.8.11-2.el7
  4. Upgrade

    Upgrade redhat/rh-python38-python-cryptography to a version that resolves this vulnerability.

    Fixed in 0:2.8-5.el7
  5. Upgrade

    Upgrade redhat/rh-python38-python-jinja2 to a version that resolves this vulnerability.

    Fixed in 0:2.10.3-6.el7
  6. Upgrade

    Upgrade redhat/rh-python38-python-lxml to a version that resolves this vulnerability.

    Fixed in 0:4.4.1-7.el7
  7. Upgrade

    Upgrade redhat/rh-python38-python-pip to a version that resolves this vulnerability.

    Fixed in 0:19.3.1-2.el7
  8. Upgrade

    Upgrade redhat/rh-python38-python-urllib3 to a version that resolves this vulnerability.

    Fixed in 0:1.25.7-7.el7
  9. Upgrade

    Upgrade redhat/python27-python to a version that resolves this vulnerability.

    Fixed in 0:2.7.18-4.el7
  10. Upgrade

    Upgrade redhat/python to a version that resolves this vulnerability.

    Fixed in 3.6.14
  11. Upgrade

    Upgrade redhat/python to a version that resolves this vulnerability.

    Fixed in 3.7.11
  12. Upgrade

    Upgrade redhat/python to a version that resolves this vulnerability.

    Fixed in 3.8.10
  13. Upgrade

    Upgrade redhat/python to a version that resolves this vulnerability.

    Fixed in 3.9.5
  14. Upgrade

    Upgrade debian/pypy3 to a version that resolves this vulnerability.

    Fixed in 7.3.11+dfsg-2+deb12u3Fixed in 7.3.19+dfsg-2Fixed in 8.0.1+dfsg-1
  15. Upgrade

    Upgrade azurelinux/python2 to a version that resolves this vulnerability.

    Fixed in 2.7.18-10

Event History

Aug 10, 2021
CVE Published
12:00 AM
Aug 18, 2021
Data Sourced
via Red Hat·04:33 PM
DescriptionSeverityAffected Software
Sep 2, 2021
Data Sourced
via Ubuntu·12:00 AM
RemedyDescriptionSeverityAffected Software
Mar 7, 2022
CVE Published
via MITRE·12:00 AM
Data Sourced
via MITRE·12:00 AM
DescriptionWeakness
Mar 10, 2022
Data Sourced
via NVD·05:42 PM
RemedyDescriptionSeverityWeaknessAffected Software
Data Sourced
via OSV·05:42 PM
DescriptionSeverity
Jun 2, 2022
Data Sourced
via Microsoft·07:00 AM
DescriptionSeverityWeaknessAffected Software

Parent advisories

This vulnerability appears in the following advisories.

Peer vulnerabilities

Found alongside the following vulnerabilities.

Frequently Asked Questions

1

What is CVE-2021-3733?

CVE-2021-3733 is a vulnerability in urllib's AbstractBasicAuthHandler class that allows an attacker to trigger a Regular Expression Denial of Service (ReDOS) during an authentication request.

2

What can an attacker do with CVE-2021-3733?

An attacker who controls a malicious HTTP server can exploit CVE-2021-3733 to launch a ReDOS attack on an HTTP client (e.g., web browser).

3

How severe is CVE-2021-3733?

CVE-2021-3733 has a severity rating of 6.5, which is considered medium.

4

Which software versions are affected by CVE-2021-3733?

CVE-2021-3733 affects Python versions 3.6.14, 3.7.11, 3.8.10, and 3.9.5, as well as other related packages.

5

How can I mitigate CVE-2021-3733?

To mitigate CVE-2021-3733, it is recommended to update to the fixed versions of Python and related packages provided by Red Hat.

Company

Resources

Contact

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