ppthtml heap-based buffer overflow

2013.11.14

Credit: Murray McAllister

Risk: High

Local: Yes

Remote: No

CVE: CVE-2013-4565

CWE: CWE-119

CVSS Base Score: 6.8/10

Impact Subscore: 6.4/10

Exploitability Subscore: 8.6/10

Exploit range: Remote

Attack complexity: Medium

Authentication: No required

Confidentiality impact: Partial

Integrity impact: Partial

Availability impact: Partial

Morning,
A heap-based buffer overflow flaw was reported in ppthtml:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=729279
Looking in xlhtml-0.5-15.fc19.src.rpm, I think the root cause of the problem is in __OLEdecode() with an under allocation here:
163 BDepot = (U8 *) malloc (0x0200 * (num_bbd_blocks + num_xbbd_blocks));
That still passes this check:
167 assert (num_bbd_blocks <= (0x0200 / 4 - 1) * num_xbbd_blocks +
168 (0x0200 / 4) - 19);
I suspect the overflow eventually occurs in this loop:
184 for (i = 0; i < num_xbbd_blocks; i++)
with:
203 fread (s, 0x0200, 1, input);
204 test_exitf (!ferror (input), 5, ends ());
205 s += 0x0200;
continually executed (but haven't tested thoroughly!!!).
Can a CVE please be assigned?
(Cc'ing Salvatore in case there is more information in the Debian report that I cannot see.)
Cheers,
--
Murray McAllister / Red Hat Security Response Team

References:

http://seclists.org/oss-sec/2013/q4/278

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=729279

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ppthtml heap-based buffer overflow

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