Disable the Windows print spooler to prevent hacks, Microsoft tells customers

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Microsoft hit one more snag in its efforts to lock down the Home windows print spooler, because the software program maker warned prospects on Thursday to disable the service to include a brand new vulnerability that helps attackers execute malicious code on absolutely patched machines.

The vulnerability is the third printer-related flaw in Home windows to return to mild up to now 5 weeks. A patch Microsoft launched in June for a distant code-execution flaw failed to repair an analogous however distinct flaw dubbed PrintNightmare, which additionally made it attainable for attackers to run malicious code on absolutely patched machines. Microsoft launched an unscheduled patch for PrintNightmare, however the repair failed to stop exploits on machines utilizing sure configurations.

Carry your individual printer driver

On Thursday, Microsoft warned of a brand new vulnerability within the Home windows print spooler. The privilege-escalation flaw, tracked as CVE-2021-34481, permits hackers who have already got the power to run malicious code with restricted system rights to raise these rights. The elevation permits the code to entry delicate elements of Home windows so malware can run every time a machine is rebooted.

“An elevation of privilege vulnerability exists when the Home windows Print Spooler service improperly performs privileged file operations,” Microsoft wrote in Thursday’s advisory. “An attacker who efficiently exploited this vulnerability might run arbitrary code with SYSTEM privileges. An attacker might then set up applications; view, change, or delete knowledge; or create new accounts with full person rights.”

Microsoft mentioned that the attacker should first have the power to execute code on a sufferer’s system. The advisory charges in-the-wild exploits as “extra probably.” Microsoft continues to advise that prospects set up the beforehand issued safety updates. A print spooler is software program that manages the sending of jobs to the printer by briefly storing knowledge in a buffer and processing the roles sequentially or by job precedence.

“The workaround for this vulnerability is stopping and disabling the Print Spooler service,” Thursday’s advisory mentioned. It gives a number of strategies prospects can use to take action.

The vulnerability was found by Jacob Baines, a vulnerability researcher at safety agency Dragos, who’s scheduled to ship a chat titled “Carry Your Personal Print Driver Vulnerability” at subsequent month’s Defcon hacker conference The manager abstract for the presentation is:

What are you able to do, as an attacker, when you end up as a low privileged Home windows person with no path to SYSTEM? Set up a weak print driver! On this speak, you will learn to introduce weak print drivers to a totally patched system. Then, utilizing three examples, you will learn to use the weak drivers to escalate to SYSTEM.”

In an electronic mail, Baines mentioned he reported the vulnerability to Microsoft in June and did not know why Microsoft revealed the advisory now.

“I used to be stunned by the advisory as a result of it was very abrupt and never associated to the deadline I gave them (August 7), nor was it launched with a patch,” he wrote. “A kind of two issues (researcher public disclosure or availability of a patch) usually prompts a public advisory. I am unsure what motivated them to launch the advisory with out a patch. That’s usually towards the purpose of a disclosure program. However individually, I’ve not publicly disclosed the vulnerability particulars and will not till August 7. Maybe they’ve seen the small print revealed elsewhere, however I’ve not.”

Microsoft mentioned it’s engaged on a patch however didn’t present a timeline for its launch.

Baines, who mentioned he carried out the analysis outdoors of his duties at Dragos, described the severity of the vulnerability as “medium.”

“It does have a CVSSv3 rating of seven.8 (or Excessive), however on the finish of the day, it is only a native privilege escalation,” he defined. “In my view, the vulnerability itself has some fascinating properties that make it worthy of a chat, however new native privilege escalation points are present in Home windows on a regular basis.”

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