CVE-2018-20852

http.cookiejar.DefaultPolicy.domain_return_ok 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.

CVSS 3.1

4.3CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N

EPSS

3.7% chance of exploitation in the next 30 days; higher than 89% of CVEs (scores of 2026-10-25)

CWE

CWE-20

Published

2019-07-13

Modified

2026-10-07

Record from

the NVD, synced 2026-10-19

Affected

• python:python

References

• http://lists.opensuse.org/opensuse-security-announce/2019-08/msg00071.html
• http://lists.opensuse.org/opensuse-security-announce/2019-08/msg00074.html
• http://lists.opensuse.org/opensuse-security-announce/2020-01/msg00040.html
• https://access.redhat.com/errata/RHSA-2019:3725
• https://access.redhat.com/errata/RHSA-2019:3948

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