Defcon Talk Prompts New Windows Print Spooler Flaw Warning

Microsoft’s problems with security defects in the Windows Print Spooler utility are getting worse by the week.

After spending the last two months pushing out multiple Print Spooler fixes (one as an emergency, out-of-band update), Redmond’s security response team late Thursday acknowledged a new, unpatched bug that exposes Windows users to privilege escalation attacks.

Close up of female hand using computer printer

Microsoft’s advisory describes an entirely new vulnerability — CVE-2021-34481 — that could be chained with another bug to launch code execution attacks.  

There is no patch available and Microsoft says the only workaround is for Windows users to stop and disable the Print Spooler service.

From the advisory:

An elevation of privilege vulnerability exists when the Windows Print Spooler service improperly performs privileged file operations. An attacker who successfully exploited this vulnerability could run arbitrary code with SYSTEM privileges. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.

An attacker must have the ability to execute code on a victim system to exploit this vulnerability.

Microsoft said the vulnerability has already been publicly disclosed and credited Dragos security researcher Jacob Baines with the discovery.

Strangely, Baines said on Twitter that Microsoft’s advisory came out of the blue and was not part of a coordinated vulnerability disclosure process.   

Baines said he reported the issue to Microsoft on June 18 and said it was unrelated to the PrintNightmare Print Spooler vulnerabilities.

The Dragos researcher plans to discuss the issue at the upcoming Defcon conference, scheduled for early August in Las Vegas.  In a talk titled Bring Your Own Print Driver Vulnerability, Baines is scheduled to talk about how to introduce vulnerable Windows print drivers to a fully patched system. 

The Defcon talk abstract reads:

What can you do, as an attacker, when you find yourself as a low privileged Windows user with no path to SYSTEM? Install a vulnerable print driver! In this talk, you’ll learn how to introduce vulnerable print drivers to a fully patched system. Then, using three examples, you’ll learn how to use the vulnerable drivers to escalate to SYSTEM.

Microsoft said it is working on a patch but did not provide a timeline for release.

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