openSUSE Security Update : glibc (openSUSE-SU-2011:0921-1)
Medium Nessus Plugin ID 75852
SynopsisThe remote openSUSE host is missing a security update.
DescriptionThe implementation of the blowfish based password hashing method had a bug affecting passwords that contain 8bit characters (e.g. umlauts).
Affected passwords are potentially faster to crack via brute-force methods (CVE-2011-2483).
SUSE's crypt() implementation supports the blowfish password hashing function (id $2a) and system logins by default also use this method.
This update eliminates the bug in the $2a implementation. After installing the update existing $2a hashes therefore no longer match hashes generated with the new, correct implementation if the password contains 8bit characters. For system logins via PAM the pam_unix2 module activates a compat mode and keeps processing existing $2a hashes with the old algorithm. This ensures no user gets locked out.
New passwords hashes are created with the id '$2y' to unambiguously identify them as generated with the correct implementation.
Note: To actually migrate hashes to the new algorithm all users are advised to change passwords after the update.
Services that do not use PAM but do use crypt() to store passwords using the blowfish hash do not have such a compat mode. That means users with 8bit passwords that use such services will not be able to log in anymore after the update. As workaround administrators may edit the service's password database and change stored hashes from $2a to $2x. This will result in crypt() using the old algorithm. Users should be required to change their passwords to make sure they are migrated to the correct algorithm.
Q: I only use ASCII characters in passwords, am I a affected in any way? A: No.
Q: What's the meaning of the ids before and after the update? A:
Before the update: $2a -> buggy algorithm
After the update: $2x -> buggy algorithm $2a -> correct algorithm $2y
-> correct algorithm
System logins using PAM have a compat mode enabled by default: $2x -> buggy algorithm $2a -> buggy algorithm $2y
-> correct algorithm
Q: How do I require users to change their password on next login? A:
Run the following command as root for each user: chage -d 0 <username>
Q: I run an application that has $2a hashes in it's password database.
Some users complain that they can not log in anymore. A: Edit the password database and change the '$2a' prefix of the affected users' hashes to '$2x'. They will be able to log in again but should change their password ASAP.
Q: How do I turn off the compat mode for system logins? A: Set BLOWFISH_2a2x=no in /etc/default/passwd
SolutionUpdate the affected glibc packages.