The mod_dav module in Apache 2.0.50 and earlier allows remote attackers to cause a denial of service (child process crash) via a certain sequence of LOCK requests for a location that allows WebDAV authoring access.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A9588
https://exchange.xforce.ibmcloud.com/vulnerabilities/17366
http://www.redhat.com/support/errata/RHSA-2004-463.html