[Dovecot] Weird Authentication behaviour
Hi guys,
we use dovecot 2.0.9 and authentication against a mysql database. Everything works fine, but we found some weird behavior when the password is e.g. testpass you also authenticate successfully with testpass123 or testpassNOT. Whatever comes after the correct password doesnt matter, the authentication is still successful.
Here are the used configs:
// auth-sql.conf.ext
passdb {
driver = sql
args = /etc/dovecot/dovecot-sql.conf.ext
}
userdb {
driver = static
args = uid=vmail gid=vmail home=/data/mail/%d/%n
}
// dovecot-sql.conf.ext
driver = mysql
connect = host=[IP] dbname=[DB] user=[USER] password=[PASS]
default_pass_scheme = CRYPT
password_query = SELECT password, login AS user FROM
v_email_accounts WHERE login='%u'
// 10-auth.conf
disable_plaintext_auth = no
auth_mechanisms = plain
!include auth-sql.conf.ext
// 10-master.conf
default_process_limit = 1000
default_client_limit = 3003
default_vsz_limit = 1024M
service imap-login {
inet_listener imap {
port = 143}
inet_listener imaps {
port = 993
ssl = yes}
service_count = 0
vsz_limit = 1024M
}
service pop3-login {
inet_listener pop3 {
port = 110}
inet_listener pop3s {
port = 995
ssl = yes}
}
service lmtp {
unix_listener lmtp {
}
}
service imap {
vsz_limit = 1024M
process_limit = 2048
}
service pop3 {
process_limit = 2048
}
service auth {
unix_listener auth-userdb {
user = vmail
group = vmail}
client_limit = 8096
}
service auth-worker {
}
service dict {
unix_listener dict {
}
}
Thanks in advance for your help!
On 03/24/2014 07:34 AM, Jürgen Ladstätter wrote:
Hi guys,
we use dovecot 2.0.9 and authentication against a mysql database. Everything works fine, but we found some weird behavior – when the password is e.g. “testpass” you also authenticate successfully with “testpass123” or “testpassNOT”. Whatever comes after the correct password doesn’t matter, the authentication is still successful. .. default_pass_scheme = CRYPT
http://wiki2.dovecot.org/Authentication/PasswordSchemes --
CRYPT: Traditional DES-crypted password in /etc/passwd (e.g. "pass" = vpvKh.SaNbR6s)
> *The traditional DES-crypt scheme only uses the first 8 characters of
Dovecot uses libc's crypt() function, which means that CRYPT is usually able to recognize MD5-CRYPT and possibly also other password schemes. See all of the *-CRYPT schemes at the top of this page. the password, the rest are ignored.* Other schemes may have other password length limitations (if they limit the password length at all).
Am 24.03.2014 12:47, schrieb Gedalya:
On 03/24/2014 07:34 AM, Jürgen Ladstätter wrote:
we use dovecot 2.0.9 and authentication against a mysql database. Everything works fine, but we found some weird behavior – when the password is e.g. “testpass” you also authenticate successfully with “testpass123” or “testpassNOT”. Whatever comes after the correct password doesn’t matter, the authentication is still successful. .. default_pass_scheme = CRYPT
http://wiki2.dovecot.org/Authentication/PasswordSchemes --
CRYPT: Traditional DES-crypted password in /etc/passwd (e.g. "pass" = vpvKh.SaNbR6s)
Dovecot uses libc's crypt() function, which means that CRYPT is usually able to recognize MD5-CRYPT and possibly also other password schemes. See all of the *-CRYPT schemes at the top of this page.
>> *The traditional DES-crypt scheme only uses the first 8 characters of the password, the rest are ignored.* Other schemes may have other password length limitations (if they limit the password length at all)
my passwords have 19 chars and my linux login does not accept only the first 8 ones, that's the state for many years now
frankly 8 chars is laughable, i recently wrote a PHP library to generate secure random passwords and for 100000 passwords get 13 collisions is way to much given that that means you have a collision every 8000 tries which means not you need 8000 in a real world attack
GENERATED: 100000 COLLISIONS: 13
Reindl Harald wrote:
Am 24.03.2014 12:47, schrieb Gedalya:
On 03/24/2014 07:34 AM, Jürgen Ladstätter wrote:
we use dovecot 2.0.9 and authentication against a mysql database. Everything works fine, but we found some weird behavior – when the password is e.g. “testpass” you also authenticate successfully with “testpass123” or “testpassNOT”. Whatever comes after the correct password doesn’t matter, the authentication is still successful. .. default_pass_scheme = CRYPT
http://wiki2.dovecot.org/Authentication/PasswordSchemes --
CRYPT: Traditional DES-crypted password in /etc/passwd (e.g. "pass" = vpvKh.SaNbR6s)
Dovecot uses libc's crypt() function, which means that CRYPT is usually able to recognize MD5-CRYPT and possibly also other password schemes. See all of the *-CRYPT schemes at the top of this page.
>>> *The traditional DES-crypt scheme only uses the first 8 characters of the password, the rest are ignored.* Other schemes may have other password length limitations (if they limit the password length at all)
my passwords have 19 chars and my linux login does not accept only the first 8 ones, that's the state for many years now
Because libc's crypt() was extended to support other encryption algorithms and your distribution chose to use them. (in Debian see for example /etc/login.defs, variable ENCRYPT_METHOD)
That doesn't change the fact you can still use crypt() with DES encryption. For example, htpasswd still does that by default (or at least was doing that few months ago), you can recofigure your Linux login to do it as well and obviously you can configure Dovecot the same way.
frankly 8 chars is laughable, i recently wrote a PHP library to generate secure random passwords and for 100000 passwords get 13 collisions is way to much given that that means you have a collision every 8000 tries which means not you need 8000 in a real world attack
GENERATED: 100000 COLLISIONS: 13
Yes, AFAIK DES encryption is obsolete for very long time and if you know hash, it's quite easy to generate a secret which will match the hash (so security-wise database with DES encrypted passwords is pretty much no better than database with plaintext passwords)
For the author of top post: Dovecot does what you told it to do. If you want to change this, it'll be a bit of a problem.
If you by any chance have plaintext passwords for your accounts (and you shouldn't have them), you can pass them to
doveadm pw -s SHA512-CRYPT -p plaintext
and store what comes out to your DB.
If you don't have them, there's a way using postlogin script - http://wiki2.dovecot.org/PostLoginScripting , see http://wiki2.dovecot.org/HowTo/ConvertPasswordSchemes
This method will however convert scheme for _first_ password that allows someone to login. So you can expect complaints from your users who use their account from two devices with different passwords (with difference after 8th character.) They will login from one device, password scheme changes and the other device will be locked out.
participants (4)
-
Gedalya
-
Jiri Bourek
-
Jürgen Ladstätter
-
Reindl Harald