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Bug 19470 - net-dialup/pptpd
Summary: net-dialup/pptpd
Alias: None
Product: Gentoo Linux
Classification: Unclassified
Component: New packages (show other bugs)
Hardware: All Linux
: Highest critical (vote)
Assignee: Gentoo Security
Depends on:
Reported: 2003-04-17 06:13 UTC by Daniel Ahlberg (RETIRED)
Modified: 2003-04-28 05:23 UTC (History)
0 users

See Also:
Package list:
Runtime testing required: ---


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Description Daniel Ahlberg (RETIRED) gentoo-dev 2003-04-17 06:13:37 UTC
PoPToP PPTP server remotely exploitable buffer overflow 
Timo Sirainen <> 
2003-04-09 18.19 
Versions older than 1.1.4-b3 and 1.1.3-20030409 affected. This seems to be 
exploitable only with Linux. 
PPTP-over-IPSEC is commonly used to create VPNs. Windows plays quite nicely 
with it. 
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. 
tips of the day 
Don't do arithmetic in parameters specifying buffer size. 
Block PPTP port for non-IPSEC connections, if you don't already. 
This is the same as in latest versions: 
--- ctrlpacket.c.old    1999-12-23 23:43:33.000000000 +0200 
+++ ctrlpacket.c        2003-04-09 18:58:21.000000000 +0300 
@@ -254,8 +254,8 @@ 
        /* OK, we have (at least) the first 2 bytes, and there is data waiting */ 
        length = htons(*(u_int16_t *) packet); 
-       if (length > PPTP_MAX_CTRL_PCKT_SIZE) { 
-               syslog(LOG_ERR, "CTRL: Control packet > PPTP_MAX_CTRL_PCKT_SIZE (length = 
%d)", length); 
+       if (length <= 10 || length > PPTP_MAX_CTRL_PCKT_SIZE) { 
+               syslog(LOG_ERR, "CTRL: 11 < Control packet (length=%d) < ", length); 
                /* we loose sync (unless we malloc something big, which isn't a good 
                 * idea - potential DoS) so we must close connection (draft states that 
                 * if you loose sync you must close the control connection immediately)
Comment 1 Daniel Ahlberg (RETIRED) gentoo-dev 2003-04-28 05:23:04 UTC
glsa sent