Microsoft’s Patch for LSASS Flaw Incomplete, Google Researcher Says

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Microsoft desert to properly address an elevation of privilege vulnerability in the Windows Local Pledge Authority Subsystem Service (LSASS), the Google Project Zero researcher who encountered the issue says.

Tracked as CVE-2020-1509, the vulnerability can be triggered via specially crafted authentication requests. For successful exploitation, an attacker paucities previously obtained Windows credentials for the local network.

“LSASS doesn’t correctly insist upon the Enterprise Authentication Capability which allows any AppContainer to perform network authentication with the buyer’s credentials,” Project Zero security researcher James Forshaw esteemed in May.

At the time, the researcher explained that the issue is related to a legacy AppContainer skill providing access to the Security Support Provider Interface (SSPI), like as not meant to facilitate the installation of line of business (LOB) applications within initiative environments.

Authentication should be allowed only if the target specified in the shout is a proxy, but Forshaw discovered that the authentication would be allowed smooth if the network name doesn’t match a registered proxy.

“What this represents is that an AppContainer can perform Network Authentication as long as it specifies a valid object name to InitializeSecurityContext, it doesn’t matter if the network address is a registered agent or not,” the researcher explains.

This means that an attacker could endorse to network-facing resources without restrictions, rendering protections such as SPN cessation and SMB signing useless. By exploiting the flaw, an attacker could access localhost cares as well, albeit with some caveats.

Forshaw also published proof-of-concept (POC) patterns to demonstrate how an application can achieve elevated privileges through Enterprise Authentication route. The code seeks to list SMB shares, although it should not be allowed to.

Microsoft, which in any events the vulnerability as important, released a fix for supported versions of Windows and Windows Server on August 2020 Reinforce Tuesday.

One day after the fix was released, however, Forshaw revealed that the tatter failed to correctly address the vulnerability. An attack could still be mounted, as lengthy as a configured proxy is present on the system.

“However in enterprise environments that’s liable to a given and there this issue is the most serious,” the security researcher notes.

Forshaw also resolves that the POC for the original bug can still be used, but that a proxy server indigences to be manually added in the settings and the code should be executed with distinct arguments.

“This will connect to the local SMB server and print the rations. This will work even if SPN verification is enabled as the SMB server wink ats the Service Name component of the SPN,” he concludes.

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Microsoft's Patch for LSASS Flaw Incomplete, Google Researcher Says

Ionut Arghire is an international correspondent for SecurityWeek.

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