#VU51604 Improper validation of certificate with host mismatch in urllib3 - CVE-2021-28363
Published: March 22, 2021
Vulnerability identifier: #VU51604
Vulnerability risk: Medium
CVSSv4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: CVE-2021-28363
CWE-ID: CWE-297
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerable software:
urllib3
urllib3
Software vendor:
shazow (Andrey Petrov)
shazow (Andrey Petrov)
Description
The vulnerability allows a remote attacker to perform MitM attack.
The vulnerability exists due to urllib3 library for Python omits SSL certificate validation in some cases involving HTTPS to HTTPS proxies. The initial connection to the HTTPS proxy (if an SSLContext isn't given
via proxy_config) doesn't verify the hostname of the certificate. This
means certificates for different servers that still validate properly
with the default urllib3 SSLContext will be silently accepted. A remote attacker can supply a valid SSL certificate for a different hostname and perform Man-in-the-Middle (MitM) attack.
Remediation
Install updates from vendor's website.