Open Redirect Vulnerability in Action Pack Ruby Gem by Ruby on Rails

CVE-2021-22903

What is CVE-2021-22903?

The Action Pack Ruby gem prior to version 6.1.3.2 is susceptible to an open redirect issue. This vulnerability arises when specially crafted Host headers combined with improperly configured 'allowed host' formats enable the Host Authorization middleware to redirect users to potentially malicious sites. If the configuration does not begin with a leading dot, strings in config.hosts are treated as regular expressions, leading to insecure requests being permitted, such as allowing 'sub-example.com' while 'config.hosts << "sub.example.com"' is configured.

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