PHP5 before 5.4.4 allows passing invalid utf-8 strings via the xmlTextWriterWriteAttribute, which are then misparsed by libxml2. This results in memory leak into the resulting output.
Exploitability
AV:NAC:LPR:NUI:NScope
S:UImpact
C:HI:NA:N7.5/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N