In Apache httpd 2.4.0 to 2.4.29, when modsession is configured to forward its session data to CGI applications (SessionEnv on, not the default), a remote user may influence their content by using a "Session" header. This comes from the "HTTPSESSION" variable name used by modsession to forward its data to CGIs, since the prefix "HTTP" is also used by the Apache HTTP Server to pass HTTP header fields, per CGI specifications.