The effectiveness of a zero-day quickly deteriorates as an attack tool after it gets discovered and patched by the affected software vendors. Within the time between the discovery of the vulnerability and the release of the fix, a bad actor might try to get the most out of his previously valuable attack assets. This is exactly what we saw in late October and early November 2016, when the espionage group Pawn Storm (also known as Fancy Bear, APT28, Sofacy, and STRONTIUM) ramped up its spear-phishing campaigns against various governments and embassies around the world. In these campaigns, Pawn Storm used a previously unknown zero-day in Adobe’s Flash (CVE-2016-7855, fixed on October 26, 2016 with an emergency update) in combination with a privilege escalation in Microsoft’s Windows Operating System (CVE-2016-7255) that was fixed on November 8, 2016.
After the fix of CVE-2016-7855 in Adobe’s Flash, Pawn Storm probably devalued the two zero-days in its attack tool portfolio. Instead of only using it against very high profile targets, they started to expose much more targets to these vulnerabilities. We saw several campaigns against still-high-profile targets since October 28 until early November, 2016.