14th Feb 2002 [SBWID-5103]
COMMAND
Exim potential local buffer overflow
SYSTEMS AFFECTED
Exim 3.34 and lower
PROBLEM
The Analyzer, Izik and Mixter of 2xs security research team
[http://2xss.com/] found :
Its looks like there is few insecure/lame programming in exim mail
server up to current version.
first lets take a look at the file:
[2xs:root:~] ls -la /usr/exim/bin/exim
-rws--x--x 1 root root 2061186 Oct 23 12:56
/usr/exim/bin/exim*
[2xs:root:~]
Suid goodie.
[2xs:w00p:/root] id
uid=1001(w00p) gid=100(users) groups=100(users)
[2xs:w00p:/root] /usr/exim/bin/exim -F `perl -e\' print \"A\" x 32770\'` -C
`perl -e\' print \"A\" x 32768\'`
Segmentation fault
[2xs:w00p:/root]
Many other argument should work as well (as long there is -C among
them)
[2xs:root:~] gdb /usr/exim/bin/exim
GNU gdb 5.0
Copyright 2000 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you
are
welcome to change it and/or distribute copies of it under certain
conditions.
Type \"show copying\" to see the conditions.
There is absolutely no warranty for GDB. Type \"show warranty\" for
details.
This GDB was configured as \"i386-slackware-linux\"...
(gdb) r -F `perl -e\' print \"A\" x 32770\'` -C `perl -e\' print \"A\" x
32768\'`
Starting program: /usr/exim/bin/exim -F `perl -e\' print \"A\" x 32770\'` -C
`perl -e\' print \"A\" x
32768\'`
Program received signal SIGSEGV, Segmentation fault.
strcpy (dest=0x820e208 \'A\' <repeats 200 times>..., src=0xbfff7b48 \'A\'
<repeats 200 times>...)
at ../sysdeps/generic/strcpy.c:40
40 ../sysdeps/generic/strcpy.c: No such file or directory.
(gdb) info registers
eax 0x48216641 1210148417
ecx 0x482166bf 1210148543
edx 0xbfffa941 -1073764031
ebx 0xbffef8d4 -1073809196
esp 0xbffeeefc 0xbffeeefc
ebp 0xbffeef00 0xbffeef00
esi 0x820e208 136372744
edi 0x3 3
eip 0x401690e4 0x401690e4
eflags 0x10286 66182
cs 0x23 35
ss 0x2b 43
ds 0x2b 43
es 0x2b 43
fs 0x0 0
gs 0x0 0
fctrl 0x37f 895
fstat 0x0 0
ftag 0xffff 65535
fiseg 0x23 35
fioff 0x4009ca84 1074383492
foseg 0x2b 43
fooff 0x400fa440 1074766912
fop 0x49b 1179
after short debugging we found that there is no overflow since the eip
register coredumped in the code segment and not in the data segment,
yet we believe that there might be a way to exploit this bug with
log_write(), we are not going to deliver a working exploit until the
vendor will research and fix this bug.
In version 3.21 and lower there is another small bug with -t flag again
non exploitable just bad programming.
SOLUTION
Note : this is NOT an official patch, but provided by the bug finder
(patch to version 3.34)
--------------C2FFD0A39E3737A0A718E02C
Content-Type: TEXT/PLAIN; CHARSET=x-user-defined; NAME=\"exim-3.34-patch.diff\"
Content-ID: <Pine.LNX.4.43.0202131118553.9724@mail.securityfocus.com>
Content-Description:
Content-Disposition: INLINE; FILENAME=\"exim-3.34-patch.diff\"
diff -Nru exim-3.34/src.old/accept.c exim-3.34/src/accept.c
--- exim-3.34/src.old/accept.c Tue Feb 12 13:40:44 2002
+++ exim-3.34/src/accept.c Tue Feb 12 13:47:33 2002
@@ -1506,7 +1506,7 @@
/* Save for comparing with next one */
-strcpy(last_message_id, message_id);
+strncpy(last_message_id, message_id, MESSAGE_ID_LENGTH); /* Fixed a one-byte overflow -- Mixter */
/* Add the current message id onto the current process info string if
it will fit. */
diff -Nru exim-3.34/src.old/deliver.c exim-3.34/src/deliver.c
--- exim-3.34/src.old/deliver.c Tue Feb 12 13:40:44 2002
+++ exim-3.34/src/deliver.c Tue Feb 12 14:15:53 2002
@@ -3704,7 +3704,7 @@
the message size. */
deliver_force = forced;
-strcpy(message_id, id);
+strncpy(message_id, id, MESSAGE_ID_LENGTH);
return_count = 0;
message_size = 0;
@@ -4083,7 +4083,8 @@
slen += 3;
}
- strcpy(h->text + slen, s);
+ /* Fixed potential remote vulnerability -- Mixter */
+ strncpy(h->text + slen, s, size-slen-1);
slen += len;
}
diff -Nru exim-3.34/src.old/host.c exim-3.34/src/host.c
--- exim-3.34/src.old/host.c Tue Feb 12 13:40:44 2002
+++ exim-3.34/src/host.c Tue Feb 12 19:19:52 2002
@@ -281,7 +281,7 @@
}
sender_fullhost =
- store_malloc((int)strlen(fullhost) + (int)strlen(rcvhost) + 2);
+ store_malloc((int)strlen(fullhost) + (int)strlen(rcvhost) + 3);
sender_rcvhost = sender_fullhost + (int)strlen(fullhost) + 1;
strcpy(sender_fullhost, fullhost);
strcpy(sender_rcvhost, rcvhost);
@@ -471,7 +471,7 @@
next = store_malloc(sizeof(ip_address_item));
next->next = NULL;
- strcpy(next->address, s);
+ strncpy(next->address, s, 46);
if (yield == NULL) yield = last = next; else
{
@@ -571,7 +571,7 @@
/* If there is no buffer, put the string into some new store. */
if (buffer == NULL) return string_copy(yield);
-strcpy(buffer, yield);
+strncpy(buffer, yield, 46);
return buffer;
}
diff -Nru exim-3.34/src.old/log.c exim-3.34/src/log.c
--- exim-3.34/src.old/log.c Tue Feb 12 13:40:44 2002
+++ exim-3.34/src/log.c Tue Feb 12 14:37:56 2002
@@ -61,6 +61,14 @@
if (!syslog_timestamp) s += 20;
len = (int)strlen(s);
+/* Added safeguard against syslog overflows -- Mixter */
+if(len > 4096)
+{
+ len = 4026;
+ memset(s+4000,0,strlen(s)-4000);
+ strcat(s, \" WARNING: Message cut off!\");
+}
+
#ifndef NO_OPENLOG
if (!syslog_open)
{
@@ -185,7 +193,7 @@
has been cycled, then open the file. The static slot for saving it is the same
size as buffer, and the text has been checked above to fit. */
-if (strcmp(name, \"main\") == 0) strcpy(mainlog_name, buffer);
+if (strcmp(name, \"main\") == 0) strncpy(mainlog_name, buffer, LOG_NAME_SIZE);
/* After a successful open, arrange for automatic closure on exec(). */
@@ -585,7 +593,7 @@
{
spaceleft = seplen + 1;
ptr = log_buffer + LOG_BUFFER_SIZE - spaceleft;
- strcpy(ptr - (int)strlen(tmsg), tmsg);
+ strncpy(ptr - (int)strlen(tmsg), tmsg, spaceleft);
}
(void)string_format(ptr, spaceleft, separator);
while(*ptr) ptr++;
diff -Nru exim-3.34/src.old/match.c exim-3.34/src/match.c
--- exim-3.34/src.old/match.c Tue Feb 12 13:40:45 2002
+++ exim-3.34/src/match.c Tue Feb 12 14:39:45 2002
@@ -876,7 +876,7 @@
\"+caseful\" in the list, it restores a caseful copy from the original address.
*/
-strcpy(address, origaddress);
+strncpy(address, origaddress, big_buffer_size);
for (p = address + ((caseless || llen < 0)? 0 : llen); *p != 0; p++)
*p = tolower(*p);
diff -Nru exim-3.34/src.old/readconf.c exim-3.34/src/readconf.c
--- exim-3.34/src.old/readconf.c Tue Feb 12 13:40:45 2002
+++ exim-3.34/src/readconf.c Tue Feb 12 14:25:01 2002
@@ -356,7 +356,7 @@
char *newbuffer;
big_buffer_size += BIG_BUFFER_SIZE;
newbuffer = store_malloc(big_buffer_size);
- strcpy(newbuffer, big_buffer);
+ strncpy(newbuffer, big_buffer, big_buffer_size-1);
store_free(big_buffer);
big_buffer = newbuffer;
if (fgets(big_buffer+newlen, big_buffer_size-newlen, config_file) == NULL)
@@ -440,7 +440,7 @@
{
int newsize = big_buffer_size + BIG_BUFFER_SIZE;
char *newbuffer = store_malloc(newsize);
- strcpy(newbuffer, big_buffer);
+ strncpy(newbuffer, big_buffer, big_buffer_size-1);
s = newbuffer + (s - big_buffer);
ss = newbuffer + (ss - big_buffer);
t = newbuffer + (t - big_buffer);
@@ -461,7 +461,7 @@
memmove(p + replen, pp, ss - pp + 1);
ss += moveby;
}
- strncpy(p, m->replacement, replen);
+ strncpy(p, m->replacement, replen-2);
t = p + replen;
}
}
@@ -2240,7 +2240,8 @@
/* Finally, try the unadorned name */
-strcpy(big_buffer, config_filename);
+/* Fixed overflow. 256 chars are maximally needed here. -- Mixter */
+strncpy(big_buffer, config_filename, big_buffer_size>256?256:big_buffer_size);
if (config_file == NULL) config_file = fopen(big_buffer, \"r\");
/* Failure to open the configuration file is a serious disaster. */
@@ -2326,7 +2327,7 @@
m->next = NULL;
m->command_line = FALSE;
if (mlast == NULL) macros = m; else mlast->next = m;
- strcpy(m->name, name);
+ strncpy(m->name, name, namelen-1); /* fixed potential overflow -- Mixter */
m->replacement = string_copy(s);
}
diff -Nru exim-3.34/src.old/tree.c exim-3.34/src/tree.c
--- exim-3.34/src.old/tree.c Tue Feb 12 13:40:46 2002
+++ exim-3.34/src/tree.c Tue Feb 12 14:30:45 2002
@@ -32,7 +32,7 @@
{
char *p = s + (int)strlen(s);
while (p > s && p[-1] != \'@\') p--;
-if (p <= s) strcpy(prepared_address, s); else
+if (p <= s) strncpy(prepared_address, s, 512); else /* fixed potential remote overflow -- Mixter */
{
char *t = prepared_address;
char *pp = p - 2;
--------------C2FFD0A39E3737A0A718E02C--
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