CVE-2018-20852: Input Validation

Published Oct 31, 2018
·
Updated

CVE-2018-20852 http.cookiejar.DefaultPolicy.domainreturnok in Lib/http/cookiejar.py in Python before 3.7.3 does not correctly validate the domain: it can be tricked into sending existing cookies to the wrong server. An attacker may abuse this flaw by using a server with a hostname that has another valid hostname as a suffix (e.g., pythonicexample.com to steal cookies for example.com). When a program uses http.cookiejar.DefaultPolicy and tries to do an HTTP connection to an attacker-controlled server, existing cookies can be leaked to the attacker. This affects 2.x through 2.7.16, 3.x before 3.4.10, 3.5.x before 3.5.7, 3.6.x before 3.6.9, and 3.7.x before 3.7.3. CVE-2014-4616 Array index error in the scanstring function in the json module in Python 2.7 through 3.5 and simplejson before 2.6.1 allows context-dependent attackers to read arbitrary process memory via a negative index value in the idx argument to the rawdecode function. CVE-2013-7040 Python 2.7 before 3.4 only uses the last eight bits of the prefix to randomize hash values, which causes it to compute hash values without restricting the ability to trigger hash collisions predictably and makes it easier for context-dependent attackers to cause a denial of service (CPU consumption) via crafted input to an application that maintains a hash table. NOTE: this vulnerability exists because of an incomplete fix for CVE-2012-1150.

Other sources

http.cookiejar.DefaultPolicy.domainreturnok in Lib/http/cookiejar.py in Python before 3.7.3 does not correctly validate the domain: it can be tricked into sending existing cookies to the wrong server. An attacker may abuse this flaw by using a server with a hostname that has another valid hostname as a suffix (e.g., pythonicexample.com to steal cookies for example.com). When a program uses http.cookiejar.DefaultPolicy and tries to do an HTTP connection to an attacker-controlled server, existing cookies can be leaked to the attacker. This affects 2.x through 2.7.16, 3.x before 3.4.10, 3.5.x before 3.5.7, 3.6.x before 3.6.9, and 3.7.x before 3.7.3.

Upstream issue:

https://bugs.python.org/issue35121

References:

https://python-security.readthedocs.io/vuln/cookie-domain-check.html

Red Hat

Python could allow a remote attacker to obtain sensitive information, caused by the failure to correctly validate the domain by http.cookiejar.DefaultPolicy.domainreturnok in Lib/http/cookiejar.py. By using a server with a hostname that has another valid hostname as a suffix, an attacker could exploit this vulnerability to obtain leaked existing cookies.

IBM

Affected Software

19 affected componentsFixes available
redhat/python<0:2.7.5-88.el7
0:2.7.5-88.el7
redhat/python3<0:3.6.8-13.el7
0:3.6.8-13.el7
redhat/python3<0:3.6.8-23.el8
0:3.6.8-23.el8
redhat/rh-python36-python<0:3.6.9-2.el6
0:3.6.9-2.el6
redhat/python27-python<0:2.7.17-2.el6
0:2.7.17-2.el6
redhat/rh-python36-python<0:3.6.9-2.el7
0:3.6.9-2.el7
redhat/python27-python<0:2.7.17-2.el7
0:2.7.17-2.el7
redhat/Python<3.4.10
3.4.10
redhat/Python<3.5.7
3.5.7
redhat/Python<3.6.9
3.6.9
redhat/Python<3.7.3
3.7.3
debian/python2.7
2.7.18-8+deb11u1
IBM Data Risk Manager<=2.0.6
Python Python>=2.0<=2.7.16
Python Python>=3.0.0<3.4.10
Python Python>=3.5.0<3.5.7
Python Python>=3.6.0<3.6.9
Python Python>=3.7.0<3.7.3
F5 BIG-IQ Centralized Management

Remediation

Information

A potentially simple workaround in the absence of patch on affected versions is to set DomainStrict in the cookiepolicy that would make sure a literal match against domain. The disadvantage would be that cookie set on example.com would not be shared with subdomain which might break workflow.

Event History

Oct 31, 2018
CVE Published
12:00 AM
Jul 13, 2019
CVE Published
via MITRE·08:29 PM
Data Sourced
via MITRE·08:29 PM
Description
May 27, 2025
Advisory Published
via F5·04:17 PM
Feb 20, 2026
Data Sourced
via Ubuntu·07:03 PM
RemedyDescriptionSeverityAffected Software
Data Sourced
via Launchpad·07:03 PM
Description
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Frequently Asked Questions

1

What is CVE-2018-20852?

CVE-2018-20852 is a vulnerability in Python before version 3.7.3 that allows an attacker to trick the cookiejar into sending existing cookies to the wrong server.

2

How severe is CVE-2018-20852?

CVE-2018-20852 has a severity rating of 5.3 (Medium).

3

Which versions of Python are affected by CVE-2018-20852?

Python versions before 3.7.3 are affected by CVE-2018-20852.

4

How can I fix CVE-2018-20852?

To fix CVE-2018-20852, upgrade your Python version to 3.7.3 or later.

5

Where can I find more information about CVE-2018-20852?

You can find more information about CVE-2018-20852 at the following references: [1] [2] [3].

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