CVE-2020-3427

The Windows Logon installer prior to 4.1.2 did not properly validate file installation paths. This allows an attacker with local user privileges to coerce the installer to write to arbitrary privileged directories. If successful, an attacker can manipulate files used by Windows Logon, cause Denial of Service (DoS) by deleting file(s), or replace system files to potentially achieve elevation of privileges. Note that this can only exploitable during new installations while the installer is running and is not exploitable once installation is finished. Versions 4.1.2 of Windows Logon addresses this issue.

Weakness

The product does not handle or incorrectly handles when it has insufficient privileges to access resources or functionality as specified by their permissions. This may cause it to follow unexpected code paths that may leave the product in an invalid state.

Affected Software

Potential Mitigations

• Compartmentalize the system to have “safe” areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area.
• Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.

References

• https://duo.com/docs/rdp-notes
• https://duo.com/docs/rdp-notes