libxml2 -- entity substitution DoS

Stefan Cornelius reports:

It was discovered that libxml2, a library providing
support to read, modify and write XML files, incorrectly
performs entity substitution in the doctype prolog, even if
the application using libxml2 disabled any entity
substitution. A remote attacker could provide a
specially-crafted XML file that, when processed, would lead
to the exhaustion of CPU and memory resources or file
descriptors.
This issue was discovered by Daniel Berrange of Red Hat.