Array index error in LightDM (aka Light Display Manager) 1.14.3, 1.16.x before 1.16.6 when the XDMCP server is enabled allows remote attackers to cause a denial of service (process crash) via an XDMCP request packet with no address.

LightDM 1.7.5 through 1.8.3 and 1.9.x before 1.9.2 does not apply the AppArmor profile to the Guest account, which allows local users to bypass intended restrictions by leveraging the Guest account.

Light Display Manager (aka LightDM) 1.4.x before 1.4.3, 1.6.x before 1.6.2, and 1.7.x before 1.7.14 uses 0664 permissions for the temporary .Xauthority file, which allows local users to obtain sensitive information by reading the file.

LightDM before 1.0.6 allows local users to change ownership of arbitrary files via a symlink attack on ~/.Xauthority.