libuser before 0.56.13-8 and 0.60 before 0.60-7, as used in the userhelper
program in the usermode package, directly modifies /etc/passwd, which
allows local users to cause a denial of service (inconsistent file state)
by causing an error during the modification. NOTE: this issue can be
combined with CVE-2015-3245 to gain privileges.

It was discovered that libuser has incomplete blacklist vulnerability. A
local user could use it to cause a denial of service.