Details
=======

Product: libtiff
Affected Versions: <= 4.0.6
Vulnerability Type: Illegel read
Vendor URL: http://www.libtiff.org/
CVE ID: CVE-2016-3631
Credit: Kaixiang Zhang of the Cloud Security Team, Qihoo 360

Introduction
Illegal read occurs in the cpStrips and cpTiles function in thumbnail.c in thumbnail allows attackers to exploit this issue to cause denial-of-service.

libtiff/tools/thumbnail.c:314.
313  for (s = 0; s < ns; s++) {
314    if (bytecounts[s] > (uint64) bufsize) {
315         buf = (unsigned char *)_TIFFrealloc(buf, (tmsize_t)bytecounts[s]);
316         if (!buf)
317             goto bad;
318         bufsize = (tmsize_t)bytecounts[s];
319      }
320      if (TIFFReadRawStrip(in, s, buf, (tmsize_t)bytecounts[s]) < 0 ||
321         TIFFWriteRawStrip(out, s, buf, (tmsize_t)bytecounts[s]) < 0) {
322         _TIFFfree(buf);
323         return 0;
324      }
325  }

gdb  --args  thumbnail  cpStrips.tif  tmpout.tif
……
Program received signal SIGSEGV, Segmentation fault.
0x0804c7bf in cpStrips (out=<optimized out>, in=0x8164530) at thumbnail.c:314
314          if (bytecounts[s] > (uint64) bufsize) {
(gdb) bt
#0  0x0804c7bf in cpStrips (out=<optimized out>, in=0x8164530) at thumbnail.c:314
#1  cpIFD (out=<optimized out>, in=<optimized out>) at thumbnail.c:378
#2  main (argc=3, argv=0xbffff384) at thumbnail.c:124
(gdb) p *bytecounts

Cannot access memory at address 0x42900001

References:
http://seclists.org/oss-sec/2016/q2/24
https://bugzilla.redhat.com/show_bug.cgi?id=1316872
http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2016-3631