The SPIP template composer/compiler in SPIP 3.1.2 and earlier allows remote authenticated users to execute arbitrary PHP code by uploading an HTML file with a crafted (1) INCLUDE or (2) INCLURE tag and then accessing it with a valider_xml action.
https://core.spip.net/projects/spip/repository/revisions/23192
https://core.spip.net/projects/spip/repository/revisions/23189
https://core.spip.net/projects/spip/repository/revisions/23186
http://www.securityfocus.com/bid/93451
http://www.openwall.com/lists/oss-security/2016/10/08/6