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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 clients 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 previously 5 weeks. A patch Microsoft released in June for a distant code-execution flaw failed to repair an identical however distinct flaw dubbed PrintNightmare, which additionally made it doable for attackers to run malicious code on absolutely patched machines. Microsoft released an unscheduled patch for PrintNightmare, however the repair failed to prevent exploits on machines utilizing sure configurations.

Convey your personal printer driver

On Thursday, Microsoft warned of a new vulnerability within the Home windows print spooler. The privilege-escalation flaw, tracked as CVE-2021-34481, permits hackers who have already got the flexibility 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 packages; view, change, or delete knowledge; or create new accounts with full consumer rights.”

Microsoft stated that the attacker should first have the flexibility to execute code on a sufferer’s system. The advisory charges in-the-wild exploits as “extra probably.” Microsoft continues to advise that clients 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 stated. It gives a number of strategies clients 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 “Bring Your Own Print Driver Vulnerability” at subsequent month’s Defcon hacker conference The chief abstract for the presentation is:

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

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

“I used to be shocked 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 type of two issues (researcher public disclosure or availability of a patch) sometimes prompts a public advisory. I am unsure what motivated them to launch the advisory with no patch. That’s sometimes in opposition to the objective 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 main points printed elsewhere, however I’ve not.”

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

Baines, who stated he carried out the analysis exterior 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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