CVE-2022-39369

phpCAS is an authentication library that allows PHP applications to easily
authenticate users via a Central Authentication Service (CAS) server. The
phpCAS library uses HTTP headers to determine the service URL used to
validate tickets. This allows an attacker to control the host header and
use a valid ticket granted for any authorized service in the same SSO realm
(CAS server) to authenticate to the service protected by phpCAS. Depending
on the settings of the CAS server service registry in worst case this may
be any other service URL (if the allowed URLs are configured to
“^(https)://.*”) or may be strictly limited to known and authorized
services in the same SSO federation if proper URL service validation is
applied. This vulnerability may allow an attacker to gain access to a
victim’s account on a vulnerable CASified service without victim’s
knowledge, when the victim visits attacker’s website while being logged in
to the same CAS server. phpCAS 1.6.0 is a major version upgrade that starts
enforcing service URL discovery validation, because there is unfortunately
no 100% safe default config to use in PHP. Starting this version, it is
required to pass in an additional service base URL argument when
constructing the client class. For more information, please refer to the
upgrading doc. This vulnerability only impacts the CAS client that the
phpCAS library protects against. The problematic service URL discovery
behavior in phpCAS < 1.6.0 will only be disabled, and thus you are not
impacted from it, if the phpCAS configuration has the following setup: 1.
phpCAS::setUrl() is called (a reminder that you have to pass in the full
URL of the current page, rather than your service base URL), and 2.
phpCAS::setCallbackURL() is called, only when the proxy mode is enabled.
3. If your PHP’s HTTP header input X-Forwarded-Host,
X-Forwarded-Server, Host, X-Forwarded-Proto, X-Forwarded-Protocol
is sanitized before reaching PHP (by a reverse proxy, for example), you
will not be impacted by this vulnerability either. If your CAS server
service registry is configured to only allow known and trusted service URLs
the severity of the vulnerability is reduced substantially in its severity
since an attacker must be in control of another authorized service.
Otherwise, you should upgrade the library to get the safe service discovery
behavior.

Bugs

• <http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1023571&gt;