The XML parser (xmlparse.c) in expat before 2.1.0 computes hash values without restricting the ability to trigger hash collisions predictably, which allows context-dependent attackers to cause a denial of service (CPU consumption) via an XML file with many identifiers with the same value.
Exploitability
AV:NAC:MAu:NImpact
C:NI:NA:P4.3/AV:N/AC:M/Au:N/C:N/I:N/A:P