Sniffing the Network

This article is intended to provide a simple demonstration of how easy it is to sniff/intercept traffic on various types of networks, and serve as a warning to utilize secure methods of communication on a) untrusted networks and b) known networks with the potential for untrusted clients or administrators. The first consideration is the topology of the network we’re connected to. To consider 5 common scenarios: Wired ethernet hub network: Hubs are becoming more and more obsolete as they are changed to switches. Multiple devices can be connected to a hub, and any data received by the hub from one device is broadcast out to all other devices. This means that all devices receive all network traffic. Not only is this an inefficient use of bandwidth, but each device is trusted to accept traffic destined for itself and to ignore traffic destined for another node. To sniff such a network, a node simply needs to switch it’s network interface card to “promiscuous mode”, meaning that it accepts all traffic received. Wired ethernet switched network: Multiple devices can be connected to a switch, however a switch has greater intelligence than a hub. The switch will inspect the traffic sent on each port, and learn the hardware (MAC) address of the client connected to a particular port. Once learned, the switch will inspect any frames it receives on a port, and forward that frame to the known recipient’s port alone. Other devices connected to the switch will not receive traffic that is not destined for them. This offers enhanced bandwidth usage over a hub. Switches rely on ARP packets which are easily forged in order to learn which devices are on which ports. Wireless open networks: Multiple devices can connect to an open wireless network. All data is broadcast across the network in plain text, and any attacker can sniff/intercept traffic being broadcast across the network. An open wireless network may present the user with a form of hotspot login page before granting internet access, however this does not detract from the network itself being open. WEP encrypted wireless network: A WEP encrypted network requires a WEP key to encrypt and decrypt network traffic. WEP has long been an outdated and insecure method of wireless network protection, and cracking a wireless network’s WEP key is fast and requires low skill. WEP is not secure. In addition, all clients connected to the network use the same WEP key to connect. That results in any user on the network with the WEP key being table to view any traffic transmitted to and from other nodes on the network. WPA/WPA2 encrypted network: A WPA/WPA2 encrypted network is significantly more secure than a WEP network. Whilst attacks exist on parts of the protocol, and extensions such as WPS, no known attack is able to recover a complex WPA/WPA2 password within an acceptable period of time. Whilst all clients connect to the network with the same password, the protocol is engineered to create different keystreams between each connected client and the access point. This means that simple sniffing in the traditional sense is not possible on the network. […]

By | December 14th, 2014|Linux, Security Consultant, Wireless|0 Comments

Linux: You may have been Compromised when..

There are a number of warning signs that a system has been compromised. The cases below warrant further investigation. Of course, they aren’t all guarantees that your system has been compromised, however they can be strong indicators. 1. Your welcome banner shows the last log in from an unknown/foreign IP address: Last login: Tue Dec 2 16:08:41 2014 from root@mt:~# 2. The load on a usually idle system is suspiciously high: root@mt:~# w 17:06:39 up 62 days, 22:37, 1 user, load average: 8.12, 8.14, 8.11 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT root pts/0 pwn 17:03 7.00s 0.00s 0.00s w This could indicate that unknown processes are running. […]

By | December 9th, 2014|Linux, Security Consultant|0 Comments

Reset Linux Root Password

There are a couple of reasons why you might want to reset a Linux root password. If the current password is known to you, just log in as root and issue the passwd command. What if you’ve forgotten the password and can’t log in? Resetting a Linux root password is simple if you have access to the machine. There are 2 main methods. Method #1 First, we boot the machine up. If LILO is in use, enter linux init=/bin/bash at the ‘LILO:’ prompt. If GRUB is in use, then press key ‘e’. We’ll need to edit the kernel line, beginning ‘linux’, and append init=/bin/sh:   […]

By | December 6th, 2014|Linux|4 Comments

Burp Suite: Intercepting & Modifying HTTP Requests & Responses

Burp Suite is a powerful web application auditor with a huge range of features, from simple to advanced. One of its core features is an intercepting proxy server. This allows us to pass our web traffic through burp suite, allowing us to view and modify both our browsers request before it goes to the remote web server, and the web server’s response before it returns to our browser. A couple common request modifications: Add data to form submissions, modify hidden fields. View and modify browser AJAX data View and edit headers including cookies And a couple of common response modifications: Remove client side JavaScript (usually validations or other limitations) Add or remove cookies sent to the browser First, fire up Burp Suite, and browse to Proxy –> Options: […]

By | December 3rd, 2014|Linux, Security Consultant|0 Comments

Linux Namespaces

Starting from kernel 2.6.24, there are 6 different types of Linux namespaces. Namespaces are useful in isolating processes from the rest of the system, without needing to use full low level virtualization technology. CLONE_NEWIPC: IPC Namespaces: SystemV IPC and POSIX Message Queues can be isolated. CLONE_NEWPID: PID Namespaces: PIDs are isolated, meaning that a PID inside of the namespace can conflict with a PID outside of the namespace. PIDs inside the namespace will be mapped to other PIDs outside of the namespace. The first PID inside the namespace will be ‘1’ which outside of the namespace is assigned to init CLONE_NEWNET: Network Namespaces: Networking (/proc/net, IPs, interfaces and routes) are isolated. Services can be run on the same ports within namespaces, and “duplicate” virtual interfaces can be created. CLONE_NEWNS: Mount Namespaces. We have the ability to isolate mount points as they appear to processes. Using mount namespaces, we can achieve similar functionality to chroot() however with improved security. CLONE_NEWUTS: UTS Namespaces. This namespaces primary purpose is to isolate the hostname and NIS name. CLONE_NEWUSER: User Namespaces. Here, user and group IDs are different inside and outside of namespaces and can be duplicated. Let’s look first at the structure of a C program, required to demonstrate process namespaces. The following has been tested on Debian 6 and 7. First, we need to allocate a page of memory on the stack, and set a pointer to the end of that memory page. We use alloca to allocate stack memory rather than malloc which would allocate memory on the heap. void *mem = alloca(sysconf(_SC_PAGESIZE)) + sysconf(_SC_PAGESIZE); Next, we use clone to create a child process, passing the location of our child stack ‘mem’, as well as the required flags to specify a new namespace. We specify ‘callee’ as the function to execute within the child space: mypid = clone(callee, mem, SIGCHLD | CLONE_NEWIPC | CLONE_NEWPID | CLONE_NEWNS | CLONE_FILES, NULL); After calling clone we then wait for the child process to finish, before terminating the parent. If not, the parent execution flow will continue and terminate immediately after, clearing up the child with it: while (waitpid(mypid, &r, 0) < 0 && errno == EINTR) { continue; } Lastly, we’ll return to the shell with the exit code of the child: if (WIFEXITED(r)) { return WEXITSTATUS(r); } return EXIT_FAILURE; Now, let’s look at the callee function: static int callee() { int ret; mount("proc", "/proc", "proc", 0, ""); setgid(u); setgroups(0, NULL); setuid(u); ret = execl("/bin/bash", "/bin/bash", NULL); return ret; } Here, we mount a /proc filesystem, and then set the uid (User ID) and gid (Group ID) to the value of ‘u’ before spawning the /bin/bash shell. […]

By | November 23rd, 2014|BASH, C/C++, Linux, Networking, Security Consultant|1 Comment

Hard Drive Data Recovery

This article discusses hard disk data recovery on Linux using dd and fdisk. I recently left for a trip to South America, and took my trusty Intenso 320GB external drive with. Well aware that I’ve dropped it a couple too many times and that it was beginning to click more and more often during regular usage, I took a full backup before leaving. There’s nothing critical on the drive that I don’t have additional copies of elsewhere, however losing it would be a pain. Having reached Madrid airport, I plugged the drive in and was about to pull some documents off it when disaster struck. The drive just clicked for about 30 seconds before Windows prompted me to format it. I tried removing it and reinserting it a couple of times but no luck – the drive had failed. I went to the duty free store in the airport and picked up a 1Tb WD Elements drive for 99 Euros, and planned to attempt data recovery when I arrived in South America. I’m keen to get the data recovery started – it’s going to take a while on my USB 2.0 laptop and the more bad sectors, the longer it will take. […]

By | November 13th, 2014|Data Recovery, Linux|4 Comments

Nginx, SSL & php5-fpm on Debian Wheezy

I decided to take a break from my love affair with Apache and set up a recent development project on Nginx. I’ve seen nothing but good things in terms of speed and performance from Nginx. I decided to set up a LEMP server (Linux, Nginx, MySQL, PHP), minus the MySQL as it’s already installed on my VM host server, and plus SSL. Here’s the full setup tutorial on Debian Wheezy: Step #1 – Installing the packages apt-get install nginx-extras mysql-client apt-get install php5-fpm php5-gd php5-mysql php-apc php-pear php5-cli php5-common php5-curl php5-mcrypt php5-cgi php5-memcached MySQL can be installed into the mix with a simple: apt-get install mysql-server […]

By | October 11th, 2014|Development, Hosting, Linux, MySQL, MySQL, PHP, PHP, PHP Articles, VPS|0 Comments

Debian Wheezy Xen + Guest Howto

Xen is usually my go to virtualization technology for Linux. Here’s a HOWTO on setting up Xen on Debian Wheezy and the first guest virtual machine. First step is getting the required packages: apt-get install xen-linux-system xen-tools xen-utils-4.1 xen-utils-common xenstore-utils xenwatch Now, we’ll need to specify the Xen kernel as the default boot kernel on the host, and then reboot: […]

By | October 8th, 2014|Linux, Networking, VPS|0 Comments

MySQL Master-Master Replication, Heartbeat, DRBD, Apache, PHP, Varnish MegaHOWTO

I created this HOWTO while building a new development environment today. The intention is to take a single Apache2/Varnish/MySQL environment and scale it to two servers, with one effectively a “hot-standby” – increase redundancy and continuity whilst maintaining current performance. This HOWTO is based on Linux Debian-76-wheezy-64-minimal 3.2.0-4-amd64 #1 SMP Debian 3.2.60-1+deb7u3 x86_64 Our current server has IP and our new server has IP Section #1: Set up MySQL Master/Master Replication First, we’ll set up MySQL master to master replication. In this configuration, data can be written and read from either host. Bear in mind that issues may exist with autoincrement fields when written to at the same time. There are other caveats with replication so ensure to research them along with how to deal with corruption and repair before considering this setup for a live application. Also be sure to be using the same version of MySQL on both servers – this may not always be necessary, however unless you are very familiar with any changes between versions, not doing so could spell disaster. […]

Linux iproute2 multiple default gateways

This article describes a Linux server set up with 2 interfaces (eth0) and (eth1). Each interface has a separate ISP, network details and default gateway. eth0 has two sets of network details on the same interface and so a virtual interface (eth0:0) must be created to handle the second IP. By default, Linux only allows for one default gateway. Let’s see what happens if we try to use multiple uplinks with 1 default gateway. Assume eth0 is assigned and eth1 is assigned Let’s say our default gateway is (which of course is found through eth0) but there’s also a gateway on eth1 which we can’t enter as Linux only allows for the one. Our routing table now looks like this: root@www1:~# route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface UG 0 0 0 eth0 U 0 0 0 eth0 U 0 0 0 eth1 If a packet comes in to us, routed through the gateway from say, our machine will receive it. When it tries to reply to however, it runs down the routing table and sees that it’s not local to eth0 or eth1 and therefore will get routed out through the default gateway ( – the problem is, this is the wrong gateway and so the target machine will ignore our response due to it being out of sequence and from the wrong IP. Using iproute2, Linux can track multiple routing tables and therefore multiple default gateways. If the packet comes in through one interface and to one IP, it will go out via a specific default gateway. The script to achieve this is as follows: […]

By | October 5th, 2014|BASH, Linux, Networking, SH/BASH|2 Comments

Debian Linux Wheezy OpenVPN & Squid3 HOWTO with Transparent Proxying

Before my last extended period travelling and using public networks, I decided to set up a new low spec virtual machine on one of my hosted servers. I trust my datacenter and their uplinks more than I trust the free WiFi and public networks I travel through, and so while all my internet traffic is being routed over an encrypted tunnel to my dedicated server, I’m a lot happier. I threw Squid3 into the mix, as it caches common assets and the sites I visit. This speeds up my web access and page load time. OpenVPN can be configured more simply with a ‘static key’ configuration, however I’ve chosen to go down the PKI route for future growth. On my new VPN server I run: apt-get install openvpn Once OpenVPN is installed, I’ll need to set up my PKI system, certificate authority (CA), server certificate (vpn) and my first client certificate (npn) […]

By | October 4th, 2014|Hosting, Linux, Networking, VPS|2 Comments

Exim, DKIM and Debian Configuration

DKIM is a system for cryptographically signing messages and confirming they were sent from a sending server authorized at domain level. A private and public key pair is generated. The private key is used to sign the messages, and the public key is published as a DNS TXT record for the domain name. This allows recipients to electronically verify that mail claiming to be from domain was actually sent by a server authorized to send mail on behalf of that domain. Implementing DKIM into a mail system increases trust and deliverability. Setting up Exim to sign outgoing mail under DKIM (Domain Keys Identified Mail) is a reasonably quick and simple task. Assuming you’re using an up to date version of Debian with Exim4, the process is even easier. […]

By | July 11th, 2014|BASH, Linux, Networking|7 Comments

PHP Local and Remote File Inclusion (LFI, RFI) Attacks

PHP supports the ability to ‘include’ or ‘require’ additional files within a script. If unsanitized data is passed to such functions, an attacker may be able to get remote code execution access to the server. A typical include block might look something like this: <?php require("config/"); require("lib/db.lib.php"); require("lib/parser.lib.php"); include("contrib/users/user.contrib.php"); die("This is a test"); ?> Now, it’s also possible to dynamically require or include files based on variables or user input, say for example: […]

By | August 15th, 2013|Linux, PHP, PHP, PHP Articles, Security Consultant|0 Comments