common/extensions/sync_helper.cc in Google Chrome before 28.0.1500.71 proceeds with sync operations for NPAPI extensions without checking for a certain plugin permission setting, which might allow remote attackers to trigger unwanted extension changes via unspecified vectors.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A17347
https://code.google.com/p/chromium/issues/detail?id=252034
http://www.debian.org/security/2013/dsa-2724
http://googlechromereleases.blogspot.com/2013/07/stable-channel-update.html