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                         Luigi Auriemma

Application: Feng
http://live.polito.it/documentation/feng
Versions: <= 0.1.15
Platforms: *nix
Bugs: A] first buffer-overflow in RTSP_valid_response_msg
B] second buffer-overflow in RTSP_valid_response_msg
C] crash in RTSP_remove_msg
D] NULL pointer in parse_transport_header
E] NULL pointer in parse_play_time_range
F] NULL pointer in log_user_agent
G] NULL pointer in Netembryo 0.0.4
Exploitation: remote
Date: 27 Dec 2007
Author: Luigi Auriemma
e-mail: [email protected]
web: aluigi.org

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1) Introduction
2) Bugs
3) The Code
4) Fix

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===============
1) Introduction

Feng is an open source RTSP/RTP streaming server written by the italian
team of the Politecnico di Torino University for the LScube project.

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=======
2) Bugs

---

A] first buffer-overflow in RTSP_valid_response_msg

A buffer-overflow vulnerability is exploitable through a stack buffer
of 15 bytes called trash used as destination by sscanf without the
needed size limits.

From rtsp/RTSP_state_machine.c:

int RTSP_valid_response_msg(unsigned short *status, char msg, RTSP_buffer * rtsp)
// This routine is from BP.
{
char ver[32], trash[15];
unsigned int stat;
unsigned int seq;
int pcnt; / parameter count */

*ver = *msg = '\0';
/* assuming "stat" may not be zero (probably faulty) */
stat = 0;

pcnt =
    sscanf(rtsp->in_buffer, " %31s %u %s %s %u\n%255s ", ver, &stat,
       trash, trash, &seq, msg);
    ...

---

B] second buffer-overflow in RTSP_valid_response_msg

A buffer-overflow vulnerability is exploitable through a stack buffer
of 100 bytes called msg used as destination by sscanf limited to 255
bytes in the function RTSP_valid_response_msg.

From rtsp/RTSP_state_machine.c:

int RTSP_handler(RTSP_buffer * rtsp)
{
unsigned short status;
char msg[100];
…
op = RTSP_valid_response_msg(&status, msg, rtsp);
…

int RTSP_valid_response_msg(unsigned short *status, char *msg, RTSP_buffer * rtsp)
…
sscanf(rtsp->in_buffer, " %31s %u %s %s %u\n%255s ", ver, &stat,
trash, trash, &seq, msg);
…

---

C] crash in RTSP_remove_msg

An integer overflow is exploitable through the RTP packets.
Using a 16 bit size value of 0xffff is possible to force the server to
move 4294967293 bytes in the destination buffer:

RTSP_BUFFERSIZE = 65536
len = 65539 (4 of hdrlen + 0xffff)
result = -3

From rtsp/RTSP_lowlevel.c:

void RTSP_remove_msg(int len, RTSP_buffer * rtsp)
{
rtsp->in_size -= len;
if (rtsp->in_size && len) { /* discard the message from the in_buffer. */
memmove(rtsp->in_buffer, &(rtsp->in_buffer[len]),
RTSP_BUFFERSIZE - len);
memset(&(rtsp->in_buffer[len]), 0, RTSP_BUFFERSIZE - len);
}
}

---

D] NULL pointer in parse_transport_header

From rtsp/RTSP_setup.c:

static RTSP_Error parse_transport_header(RTSP_buffer * rtsp,
…
p = strstr(p, "=");
sscanf(p + 1, "%d", &(cli_ports.RTP));
p = strstr(p, "-");
sscanf(p + 1, "%d", &(cli_ports.RTCP));
…
p = strstr(p, "=");
sscanf(p + 1, "%d", &rtp_ch);
…
p = strstr(p, "=");
sscanf(p + 1, "%d", &rtp_ch);
…

---

E] NULL pointer in parse_play_time_range

From rtsp/RTSP_Play:

static RTSP_Error parse_play_time_range(RTSP_buffer * rtsp, play_args * args)
…
q = strchr(q, '=');
if (get_utc(&(args->playback_time), q + 1) != ERR_NOERROR) {
…

---

F] NULL pointer in log_user_agent

The log_user_agent function uses an unchecked strstr for finding the
end of the User-Agent value (a line field), but the server can handle
also carriage-return chars allowing an attacker to crash it using only
0x0d chars in his request.

From rtsp/RTSP_utils.c:

void log_user_agent(RTSP_buffer * rtsp)
{
char * p;

if ((p = strstr(rtsp->in_buffer, HDR_USER_AGENT)) != NULL) {
    char cut[strlen(p)];
    strcpy(cut, p);
    p = strstr(cut, "\n");
    cut[strlen(cut) - strlen(p) - 1] = '\0';
    ...

---

G] NULL pointer in Netembryo 0.0.4

Although this vulnerability affects another software of the LScube
project I have preferred to include it here since only when used with
Feng this bug can be considered a security bug (Netembryo in fact is
used also in libnemesi which is a client-side library).

The usage of the ':' char after the backslash allows an attacker to
crash the server on which is used the Url_init() function of the
Netembryo library.
In short when an urlname like /: is used the port_begin and path_begin
pointers will point to the same location bypassing the check
"port_begin > path_begin", then the function will try to allocate
4294967294 bytes (-2 resulted by (size_t)(path_begin - port_begin - 1))
for url->port which will fail and so the resulted NULL pointer will be
used as destination in the subsequent strncpy.

From utils/url.c:

int Url_init(Url * url, char * urlname)
{
…
path_begin = strstr(hostname_begin, "/");
if (path_begin == NULL) {
path_len = 0;
}
else {
++path_begin;
…
port_begin = strstr(hostname_begin, ":");
if ((port_begin == NULL) || ((port_begin > path_begin) && (path_begin != NULL))) {
…
if (port_len) {
url->port = (char*)malloc(port_len+1);
strncpy(url->port, port_begin, port_len);
url->port[port_len] = '\0';
}
…

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3) The Code

http://aluigi.org/poc/fengulo.zip

nc SERVER 554 -v -v < bof1.txt
…
nc SERVER 554 -v -v < netembry0.txt

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4) Fix

The bugs will be fixed in the next days.

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Luigi Auriemma
http://aluigi.org