The encoder_contexte_ajax function in ecrire/inc/filtres.php in SPIP 2.x before 2.1.19, 3.0.x before 3.0.22, and 3.1.x before 3.1.1 allows remote attackers to conduct PHP object injection attacks and execute arbitrary PHP code via a crafted serialized object.
https://core.spip.net/projects/spip/repository/revisions/22903