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Home » Hacking News » Gentoo 200304-08: PPTP buffer overflow

Gentoo 200304-08: PPTP buffer overflow

by Nikola Strahija on April 30th, 2003 A vulnerability has been found in the PPTP-over-IPSEC package. The problem lies in the packet header part of PPTP.


-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

- - - ---------------------------------------------------------------------
GENTOO LINUX SECURITY ANNOUNCEMENT 200304-08
- - - ---------------------------------------------------------------------

PACKAGE : pptpd
SUMMARY : buffer overflow
DATE : 2003-04-28 09:22 UTC
EXPLOIT : remote
VERSIONS AFFECTED : FIXED VERSION : >=pptpd-1.1.3.20030429
CVE : CAN-2003-0213

- - - ---------------------------------------------------------------------

- - From advisory:

"PPTP packet header contain 16bit length which specifies the full size of
the packet:

bytes_this = read(clientFd, packet + bytes_ttl, 2 - bytes_ttl);
// ...
bytes_ttl += bytes_this;
// ...
length = htons(*(u_int16_t *) packet);
if (length > PPTP_MAX_CTRL_PCKT_SIZE) {
// abort
}

Looks good so far, except:

bytes_this = read(clientFd, packet + bytes_ttl, length - bytes_ttl);

If given length was 0 or 1, the "length - bytes_ttl" result is -1 or -2,
which means that it reads unlimited amount of data from client into
"packet", which is a buffer located in stack.

The exploitability only depends on if libc allows the size parameter to be
larger than SSIZE_MAX bytes. GLIBC does, Solaris and *BSD don't."

Read the full advisory at:
http://marc.theaimsgroup.com/?l=bugtraq&m=104994375011406&w=2

SOLUTION

It is recommended that all Gentoo Linux users who are running
net-dialup/pptpd upgrade to pptpd-1.1.3.20030409 as follows:

emerge sync
emerge pptpd
emerge clean

- - - ---------------------------------------------------------------------
[email protected] - GnuPG key is available at http://cvs.gentoo.org/~aliz
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