It was discovered that CUPS didn"t properly handle adding a large number of RSS subscriptions. A local user could exploit this and cause CUPS to crash, leading to a denial of service. This issue only applied to Ubuntu 7.10, 8.04 LTS and 8.10. It was discovered that CUPS did not authenticate users when adding and cancelling RSS subscriptions. An unprivileged local user could bypass intended restrictions and add a large number of RSS subscriptions. This issue only applied to Ubuntu 7.10 and 8.04 LTS. It was discovered that the PNG filter in CUPS did not properly handle certain malformed images. If a user or automated system were tricked into opening a crafted PNG image file, a remote attacker could cause a denial of service or execute arbitrary code with user privileges. In Ubuntu 7.10, 8.04 LTS, and 8.10, attackers would be isolated by the AppArmor CUPS profile. It was discovered that the example pstopdf CUPS filter created log files in an insecure way. Local users could exploit a race condition to create or overwrite files with the privileges of the user invoking the program. This issue only applied to Ubuntu 6.06 LTS, 7.10, and 8.04 LTS