CVE-2018-20852
MediumCVSS 4.3Exploitation Probability (EPSS)
High risk89th percentile - higher than 89% of all known CVEs
Summary
http.cookiejar.DefaultPolicy.domain_return_ok in Python before 3.7.3 does not correctly validate the domain, allowing existing cookies to be sent to the wrong server. An attacker may abuse this 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). 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.
Risk Assessment
User cookies may leak to an attacker controlling a server with a similar hostname, potentially leading to session hijacking or unauthorized account access.
Recommendation
Upgrade Python to a fixed version (e.g., 3.7.3+ or the appropriate version for your branch) and review cookie handling configuration in applications.
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Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS

