The (1) update and (2) package-installation features in MODX Revolution 2.5.4-pl and earlier use http://rest.modx.com by default, which allows man-in-the-middle attackers to spoof servers and trigger the execution of arbitrary code by leveraging the lack of the HTTPS protection mechanism.
setup/templates/findcore.php in MODX Revolution 2.5.4-pl and earlier allows remote attackers to execute arbitrary PHP code via the corepath parameter.
setup/controllers/language.php in MODX Revolution 2.5.4-pl and earlier does not properly constrain the language parameter, which allows remote attackers to conduct Cookie-Bombing attacks and cause a denial of service (cookie quota exhaustion), or conduct HTTP Response Splitting attacks with resultant XSS, via an invalid parameter value.
setup/controllers/welcome.php in MODX Revolution 2.5.4-pl and earlier allows remote attackers to execute arbitrary PHP code via the configkey parameter to the setup/index.php?action=welcome URI.
The (1) update and (2) package-installation features in MODX Revolution 2.5.4-pl and earlier do not verify X.509 certificates from SSL servers, which allows man-in-the-middle attackers to spoof servers and trigger the execution of arbitrary code via a crafted certificate.