It was the second time in the last six weeks that Adobe fixed a flaw in Download Manager, the program it installs on PCs when customers download Reader or Flash Player.
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The bug, Adobe acknowledged in an advisory, "potentially allow[s] an attacker to download and install unauthorized software onto a user's system."
Israeli security researcher Aviv Raff disclosed the vulnerability last week, when he said that attackers could use the Download Manager to forcibly download and install any executable file, including attack code.
"If you go to Adobe's Web site to install a security update for Flash, you really expose yourself to a zero-day attack," Raff said.
Download Manager is not the update mechanism for Reader and Flash Player -- that's dubbed Adobe Updater -- but instead oversees file transfers from Adobe's site.
Among other things, the manager resumes interrupted downloads and queues up multiple files for download. The utility isn't an Adobe product, but rather a customized version of getPlus+, licensed from NOS Microsystems.
Although Download Manager is automatically removed from a Windows PC the next time the machine is restarted, Raff said it still posed a danger because some systems remain powered on for days or even weeks between reboots.
"Adobe recommends users verify that a potentially vulnerable version of the Adobe Download Manager is no longer installed on their machine," said Adobe in the advisory.
The steps Adobe urged involved searching the hard drive for a "C:\Program Files\NOS\" folder, or entering "services.msc" at a command line prompt in Windows, then deleting the "getPlus Helper" service from the ensuing list.
Users don't need to take any action with either Reader or Flash Player, said Adobe, as the vulnerability does not affect either program.
This wasn't the first time that a Download Manager component required patching. One of the six critical bugs Abode patched in Reader and Acrobat last month was within the NOS Microsystem's ActiveX control that allowed Internet Explorer to use Download Manager. The vulnerability had been reported to Adobe by Will Dormann, a researcher at the CERT Coordinating Center, last November.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer or subscribe to Gregg's RSS feed. His e-mail address is firstname.lastname@example.org.
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This story, "Adobe patches critical bug in Flash, Reader download tool" was originally published by Computerworld.