New Windows print spooler zero day exploitable via remote print web server …


Another zero day susceptability in Windows Print Spooler can provide a risk star management opportunities on a Windows device via a remote web server under the enemy’s control as well as the ‘Queue-Specific Files’ function.

Last month, a safety scientist inadvertently disclosed a zero-day Windows print spooler susceptability referred to as Print Nightmare that Microsoft tracks as CVE-2021-34527.

Exploiting this susceptability allows a risk star boost opportunities on an equipment or implement code from another location.

Microsoft launched a safety and security upgrade to deal with the susceptability however scientists figured out that the spot might be bypassed under specific problems.

Since the insufficient repair, safety and security scientists have actually been greatly inspecting the Windows printing APIs as well as have actually located even more susceptabilities impacting the Windows print spooler.

Remote print web server made use of in strike

Security scientist as well as Mimikatz maker Benjamin Delpy has actually openly revealed a new zero-day susceptability that permits a risk star to conveniently accomplish SYSTEM opportunities on a Windows device via a remote print web server under their control.

In a discussion with BleepingComputer, Delpy stated that his manipulate utilizes the ‘Queue-Specific Files‘ function of the Windows Point and Print capability to instantly download and install as well as implement a destructive DLL when a customer attaches to a print web server under an enemy’s control.

“At printer installation time, a vendor-supplied installation application can specify a set of files, of any type, to be associated with a particular print queue,” discusses Microsoft’s paperwork on the ‘Queue-Specific Files‘ function.

“The files are downloaded to each client that connects to the print server.”

To manipulate the susceptability, the scientist produced a print web server available over the Internet with 2 common printers that utilize the queue-specific data include.

Queue-specific files registry configuration
Queue- particular data pc registry setup
Source: Delpy

When performing the destructive DLL, it will certainly keep up SYSTEM opportunities as well as might be made use of to run any kind of command on the computer system.

Will Dormann, a susceptability expert for CERT/CC, has actually launched an advising for this susceptability that gives additional details.

“While Windows enforces that driver packages themselves are signed by a trusted source, Windows printer drivers can specify queue-specific files that are associated with the use of the device. For example, a shared printer can specify a CopyFiles directive for arbitrary ICM files,” the new CERT advisory discusses.

“These files, which are copied over with the digital-signature-enforced printer driver files are not covered by any signature requirement. That is, any file can be copied to a client system via Point and Print printer driver installation, where it can be used by another printer with SYSTEM privileges.”

“This allows for LPE on a vulnerable system.”

What makes this susceptability so harmful is that it influences all present variations of Windows as well as permits a risk star to obtain minimal accessibility to a network as well as promptly accomplish SYSTEM opportunities on the at risk tool.

Using this accessibility, hazard stars can spread out side to side via the network up until they access to a domain name controller.

A video clip showing this strike was shown to BleepingComputer as well as showed listed below.

Delpy has created a publicly accessible remote print server that can be made use of to examine the susceptability showed over.

Mitigating the new printer susceptability

The great information is that Delpy as well as Dormann have actually shared 2 techniques that can be made use of to minimize this new ‘Queue- particular data’ susceptability.

Both of these techniques are described in the CERT advisory.

Option 1: Block outgoing SMB website traffic at your network border

As Delpy’s public manipulate utilizes a remote print web server, you can obstruct outgoing SMB website traffic to avoid accessibility to the remote computer system.

However, Dormann mentions that the MS-WPRN can additionally be made use of to set up motorists without utilizing SMB, as well as hazard stars might still utilize this strategy with a regional printer web server.

Therefore, this reduction is not a secure approach of obstructing the manipulate.

Option 2: Configure PackagePoint AndPrint ServerList

A much better method to avoid this manipulate is to limit Point as well as Print to a listing of authorized web servers utilizing the ‘Package Point as well as print – Approved web servers’ team plan.

Package Point and print - Approved servers group policy
Package Point as well as print – Approved web servers team plan

This plan protects against non-administrative customers from setting up print motorists utilizing Point as well as Print unless the print web server gets on the authorized checklist.

Using this team plan will certainly offer the very best security versus the recognized manipulate.

BleepingComputer has actually spoken to Microsoft concerning the concern however has actually not listened to back.

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