CVE-2018-20852
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).
Does this matter?
Lower severity and a low EPSS score (3.67%). Track it; it rarely justifies an emergency change on its own.
Description
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
- 4.3 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
- EPSS
- 3.67% probability · 90th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-20
- Affected
- python/python
- Source
- cve@mitre.org
EPSS 3.7% since 27 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
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
- https://bugs.python.org/issue35121Exploit, Issue Tracking, Vendor Advisory
- https://lists.debian.org/debian-lts-announce/2019/08/msg00022.html
- https://lists.debian.org/debian-lts-announce/2019/08/msg00040.html
- https://lists.debian.org/debian-lts-announce/2020/07/msg00011.html
- https://lists.debian.org/debian-lts-announce/2020/08/msg00034.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/COATURTCY7G67AYI6UDV5B2JZTBCKIDX/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/K7HNVIFMETMFWWWUNTB72KYJYXCZOS5V/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZBTGPBUABGXZ7WH7677OEM3NSP6ZEA76/
- https://python-security.readthedocs.io/vuln/cookie-domain-check.htmlVendor Advisory
- https://security.gentoo.org/glsa/202003-26
- https://usn.ubuntu.com/4127-1/
- https://usn.ubuntu.com/4127-2/
- https://www.oracle.com/security-alerts/cpuapr2020.html
- 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
- https://bugs.python.org/issue35121Exploit, Issue Tracking, Vendor Advisory
- https://lists.debian.org/debian-lts-announce/2019/08/msg00022.html
- https://lists.debian.org/debian-lts-announce/2019/08/msg00040.html
- https://lists.debian.org/debian-lts-announce/2020/07/msg00011.html
- https://lists.debian.org/debian-lts-announce/2020/08/msg00034.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/COATURTCY7G67AYI6UDV5B2JZTBCKIDX/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/K7HNVIFMETMFWWWUNTB72KYJYXCZOS5V/
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.