Local vulnerability in libutil derived with FreeBSD 4.4-RC (and earlier)

From: Przemyslaw Frasunek (venglinat_private)
Date: Thu Sep 20 2001 - 12:48:34 PDT

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    Hello,

OpenSSH derived with FreeBSD 4.4 (and earlier) doesn't drop privileges
before messing with login class capability database. The most problematic
is:

        if (newcommand == NULL && !quiet_login && !options.use_login) {
                fname = login_getcapstr(lc, "copyright", NULL, NULL);
                if (fname != NULL && (f = fopen(fname, "r")) != NULL) {
                        while (fgets(buf, sizeof(buf), f) != NULL)
                                fputs(buf, stdout);
                                fclose(f);

and

                f = fopen(login_getcapstr(lc, "welcome", "/etc/motd",
                    "/etc/motd"), "r");
[...]
                        while (fgets(buf, sizeof(buf), f))
                                fputs(buf, stdout);
                        fclose(f);

in session.c, which allows to read ANY file in system with superuser
privileges, by defining:

default:\
 :copyright=/etc/master.passwd:

or

 :welcome=/etc/master.passwd:

in user's ~/.login_conf.

login(1), which is suid and spawned by telnetd also is vulnerable to similar
attack:

        if (!rootlogin)
                auth_checknologin(lc);
[...]
        (void)setegid(pwd->pw_gid);
        (void)seteuid(rootlogin ? 0 : pwd->pw_uid);

Checking for nologin is performed with superuser privileges.
auth_checklogin() is libutil function which displays nologin file, as
defined in login capability database. User can read ANY file in system by
defining:

default:\
 :nologin=/etc/master.passwd:

FreeBSD core team has been aleady informed and official patches were
incorporated into CVS repository *before* 4.4-RELEASE, although 4.4-RC and
earlier verions are vulnerable and needs to be patched with:

http://www.freebsd.org/cgi/cvsweb.cgi/~checkout~/src/lib/libutil/login_cap.c
?rev=1.17.2.3&content-type=text/plain

Official advisory is pending. It's possible, that other *BSD systems,
supporting login capability database are also vulnerable.

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