Research on Patch Deployment
New research indicates that it’s very hard to completely patch systems against vulnerabilities:
It turns out that it may not be that easy to patch vulnerabilities completely. Using WINE, we analyzed the patch deployment process for 1,593 vulnerabilities from 10 Windows client applications, on 8.4 million hosts worldwide [Oakland 2015]. We found that a host may be affected by multiple instances of the same vulnerability, because the vulnerable program is installed in several directories or because the vulnerability is in a shared library distributed with several applications. For example, CVE-2011-0611 affected both the Adobe Flash Player and Adobe Reader (Reader includes a library for playing .swf objects embedded in a PDF). Because updates for the two products were distributed using different channels, the vulnerable host population decreased at different rates, as illustrated in the figure on the left. For Reader patching started 9 days after disclosure (after patch for CVE-2011-0611 was bundled with another patch in a new Reader release), and the update reached 50% of the vulnerable hosts after 152 days.
For Flash patching started earlier, 3 days after disclosure, but the patching rate soon dropped (a second patching wave, suggested by the inflection in the curve after 43 days, eventually subsided as well). Perhaps for this reason, CVE-2011-0611 was frequently targeted by exploits in 2011, using both the .swf and PDF vectors.