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ISP PASSWORD SECURITY
The plaintext passwords entered via the "Account Data" option in xisp
are encrypted using the encrypt/setkey routines. Since this requires a
key kept inside the executable, someone having access to the source
can potentially decode users' .xisprc entries and obtain plaintext
passwords for ISP accounts. Since the .xisprc file is created as
readable only by its owner, this is not very likely, but nevertheless,
in the interest of enhancing the security just a bit more, the
administrator installing xisp is urged to change the key saved in the
pkey[] variable, in pcode.c. The key saved there has already been
scrambled by XORing it with 0xFF so that the key string is not
traceable in the xisp binary. In order to change the key, pick a
string of 8 characters, XOR them with 0xFF and place them in pkey[].
The above is by no means a "secure system". It will deter the
"professional user" but not your average "amateur hacker" ;) But
that's OK given the scope of this package. The requirement was basically
to keep plaintext passwords from appearing in the .xisprc file. Anyone
is welcome to come up with something better (perhaps even more portable)
and contribute it to the package :)
As of version 1.9, simple PAP support was added by using the +ua pppd
option (only up to and including version 2.2.0f; this option has been
removed from pppd v2.3.x). This requires that pppd has access to a
simple file containing the username and plaintext password. To this end,
a temporary file called .xisppap is generated by xisp in the user's
home directory just prior to launching pppd, and is deleted when pppd
reads its parameters and forks to run in the background. Thus, the file
remains in the filesystem only for the time between invocation and
forking, which is about a couple of seconds on a lightly loaded system.
It is created u+rw,go-rw (mode 600) of course!
SYSTEM SECURITY
Since version 2.3, the ip-up and ip-down scripts supplied with xisp have
enhanced security. They both make use of the xispid utility derived from
the GNU id(1) program. After command line parsing is done, ip-up/ip-down
call xispid to find the real group-id of the user who started pppd. If
the user is not a member of the uucp group ("dialout" group for Debian
Linux or "root" group for Red Hat Linux) then both scripts exit, as most
likely this is a system security attack. Please note that this measure
is an enhancement and *NOT* a complete solution, as we are assuming that
the uucp (or dialout or root) group members can be trusted. Such a
"trusted" user can, conceivably, append data to privileged system files
by appropriately modifying the string passed to ip-up/ip-down via the
ipparam pppd option.
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