CVE-2019-3556

HHVM supports the use of an “admin” server which accepts administrative
requests over HTTP. One of those request handlers, dump-pcre-cache, can be
used to output cached regular expressions from the current execution
context into a file. The handler takes a parameter which specifies where on
the filesystem to write this data. The parameter is not validated, allowing
a malicious user to overwrite arbitrary files where the user running HHVM
has write access. This issue affects HHVM versions prior to 4.56.2, all
versions between 4.57.0 and 4.78.0, as well as 4.79.0, 4.80.0, 4.81.0,
4.82.0, and 4.83.0.