The Taliban's victory in Afghanistan.
The effective collapse of Afghanistan's government last Sunday and the country's general fall to the Taliban represent a humanitarian disaster. From the US point-of-view, it seems to have been more policy failure than intelligence failure. The Taliban's ascendancy may also augur an increase in newly emboldened Islamist activity in cyberspace. Historically that had been largely concentrated on recruitment and operational planning (against both of which law enforcement and counter-terrorism authorities enjoyed some success), then on radicalization and inspiration (harder to restrain), and, of course, on website defacement.
The immediate and forthcoming human toll of the Taliban's success has rightly dominated coverage of the news from that country, but it's worth mentioning another, secondary risk: the threat to sensitive data the events present. The Washington Post observes that the US probably removed, rendered inaccessible in secure clouds, or simply destroyed data it held as its forces withdrew (and destruction can take many forms, including consumption by fire; see pages 2-13 and 2-14 of TC 3-23.30 for the uses of thermite). But the large amounts of information the US shared with the now-deposed Afghan government are almost certainly now in Taliban hands.
Among the material seized by the Taliban in Afghanistan are biometric registration and identification devices that had been used by the former government, the Intercept reports. The Handheld Interagency Identity Detection Equipment (HIIDE, for short) was used for such tactical purposes as checkpoint control and also in broader programs, like the preparation of identity documents. The biometric modalities collected by HIIDE include iris scans and fingerprints; the larger centralized databases to which the devices were connected held (and possibly still hold) biographical information on a large number of individuals whose biometrics had been registered by HIIDE.
As has been widely foreseen, the Taliban victory in Afghanistan has been generally celebrated in extreme Islamist quarters of the Internet. The Wall Street Journal has an overview of the relevant activity in social media. The faithful remnant of al-Qaeda (an ally the Taliban never repudiated) has been particularly prominent, seeing in the fall of Kabul a vindication of their patient endurance.
As social media platforms consider how to respond to the Taliban conquest of Afghanistan, the Washington Post says that the Taliban itself seems to be punctiliously toeing the line drawn by those platforms' terms and conditions.