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Vulnerability fingerd Affected FreeBSD 4.1.1-RELEASE i386 Description Przemyslaw Frasunek found following. If finger takes full path name as user name, it prints out contents of that file. Because fingerd executes finger as local information provider, finger /path/to/file@some.host prints /path/to/file at some.host. finger /path/to/file@some.host Shortly before the release of FreeBSD 4.1.1, code was added to finger(1) intended to allow the utility to send the contents of administrator-specified files in response to a finger request. However the code incorrectly allowed users to specify a filename directly, the contents of which would be returned to the user. The finger daemon usually runs as user 'nobody' and invokes the finger(1) command in response to a remote request, meaning it does not have access to privileged files on the system (such as the hashed password file /etc/master.passwd), however the vulnerability may be used to read arbitrary files to which the 'nobody' user has read permission. This may disclose internal information including information which may be used to mount further attacks against the system. Note that servers running web and other services often incorrectly run these as the 'nobody' user, meaning this vulnerability may be used to read internal web server data such as web server password files, the source code to cgi-bin scripts, etc. Solution Disable the finger protocol in /etc/inetd.conf: make sure the /etc/inetd.conf file does not contain the following entry uncommented (i.e. if present in the inetd.conf file it should be commented out as shown below): #finger stream tcp nowait/3/10 nobody /usr/libexec/fingerd fingerd -s On IPv6-connected systems, be sure to disable the IPv6 instance of the finger daemon as well: #finger stream tcp6 nowait/3/10 nobody /usr/libexec/fingerd fingerd -s Solution is one of the following: 1) Upgrade your vulnerable FreeBSD system to 4.1.1-STABLE dated after the correction date. 2) Apply the patch below and rebuild your fingerd binary. Index: finger.c =================================================================== RCS file: /home/ncvs/src/usr.bin/finger/finger.c,v retrieving revision 1.15.2.3 retrieving revision 1.21 diff -u -r1.15.2.3 -r1.21 --- finger.c 2000/09/15 21:51:00 1.15.2.3 +++ finger.c 2000/10/05 15:56:13 1.21 @@ -293,6 +293,16 @@ goto net; /* + * Mark any arguments beginning with '/' as invalid so that we + * don't accidently confuse them with expansions from finger.conf + */ + for (p = argv, ip = used; *p; ++p, ++ip) + if (**p == '/') { + *ip = 1; + warnx("%s: no such user", *p); + } + + /* * Traverse the finger alias configuration file of the form * alias:(user|alias), ignoring comment lines beginning '#'. */ @@ -323,11 +333,11 @@ * gathering the traditional finger information. */ if (mflag) - for (p = argv; *p; ++p) { - if (**p != '/' || !show_text("", *p, "")) { + for (p = argv, ip = used; *p; ++p, ++ip) { + if (**p != '/' || *ip == 1 || !show_text("", *p, "")) { if (((pw = getpwnam(*p)) != NULL) && !hide(pw)) enter_person(pw); - else + else if (!*ip) warnx("%s: no such user", *p); } } Problem persists only in 4.x branch. Of course, it allows also to traverse directory structures. This has been corrected in 2000-10-05 (4.1.1-STABLE). FreeBSD 4.1-RELEASE, 4.0-RELEASE, 3.5.1-RELEASE and FreeBSD 4.1-STABLE systems dated before 2000-09-01 or after 2000-10-05 are unaffected by this vulnerability.