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Today I have stumbled upon an interesting technique from the Cisco Blog and Cisco Support Forum which is about defending an SQL injection using IPS, ASA or IOS firewall. I will concentrate on the ASA here to show you what you can do with this great device. Ofcourse what I will show works only for specific SQL attacks and is not an “ALL IN ONE” mechanism for preventing all SQL attacks. You should have a web application firewall in addition to ASA in my opinion if you want to have a full blown SQL and Web Application protection.

So basically the ASA uses regular expressions (regex) together with Modular Policy Framework to inspect specific HTTP data patterns in order to detect the SQL injection attack. It will basically check for the SQL command “UNION ALL SELECT”.

Below is the configuration as described on the Cisco support forum:

regex SQL_regex_1 “[uU][nN][iI][oO][nN]([%]2[0bB]|[+])([aA][lL][lL]([%]2[0bB]|[+]))?[sS][eE][lL][eE][cC][tT]“
regex SQL_regex_2 “[Ss][Ee][Ll][Ee][Cc][Tt](%2[0bB]|+)[^\r\x00-\x19\x7f-\xff]+(%2[0bB]|+)[Ff][Rr][Oo][Mm](%2[0bB]|+)”
class-map WebServers
match port tcp eq www
class-map type inspect http match-any SQL-map
match request body regex SQL_regex_1
match request body regex SQL_regex_2
policy-map type inspect http drop-SQL
body-match-maximum 3000
class SQL-map
drop-connection log
policy-map SQL-traffic
class WebServers
inspect http drop-SQL
service-policy SQL-traffic interface outside

We assume that our webserver is protected on a DMZ zone on the ASA. Traffic is coming from the outside so the service policy (SQL-traffic) is applied on the outside. Upon a regular expression match, the ASA will drop the HTTP connection and generate a log. The above is a just a starting point for SQL attack protection and can not defend against all attacks. For example if the SQL statement is Hex encoded or url encoded by the attacker, the regex will not detect it. Here is the link from Cisco forum for more information:

Upgrading Memory of Cisco ASA Firewall

After the introduction of Cisco ASA software version 8.3 last year, the device’s memory requirements for low-end models have been doubled. Many firewall administrators have been discouraged from this move from Cisco because they had to upgrade their firewalls RAM memory in order to upgrade to the newest versions. Upgrading the memory not only costs money but it imposes an operational hassle as well (network downtime, need to open-up the chassis etc). I get many questions from my readers about memory upgrade guides, so the links below might be helpful for some of you.

The following table shows the new memory requirements for all Cisco ASA 5500 models for software version 8.3 and later:

Cisco ASA Memory Requirements

The following video from Cisco shows you how to upgrade the memory chip on a Cisco ASA 5510 Firewall.

Upgrade Memory on Cisco ASA 5510 – Video

The following post from ccsplab shows some information for upgrading both the RAM and Flash memory on a Cisco ASA 5505 model.

Upgrade RAM and Flash on Cisco ASA 5505

The ASA 5500 series firewall can work as DHCP relay agent which means that it receives DHCP requests from clients on one interface and forwards the requests to a DHCP server on another interface. Usually the DHCP server is located in the same layer 3 subnet with its clients. There are situations however where we have only one DHCP server but several layer 3 networks exist (on different security zones on a Cisco ASA) and dynamic IP allocation is required for those networks as well. With the DHCP relay feature, we can connect the DHCP server on one network zone and have the firewall forward all DHCP requests from the other network zones to the DHCP server.


The diagram below illustrates a simple network scenario with three security zones (network interfaces) and a single DHCP server. The three network zones are inside, outside and DMZ. The DHCP clients are connected to the inside network and the DHCP server on the DMZ network. The DHCP requests from the clients on the inside network will be relayed to the server on the DMZ network. The server will assign IP addresses in the range to the clients.


!First identify the DHCP server and the interface it Is connected to
ciscoasa# conf t
ciscoasa(config)# dhcprelay server DMZ
ciscoasa(config)# dhcprelay timeout 90

!Now enable the DHCP relay on the inside interface
ciscoasa(config)# dhcprelay enable inside

!Assign the ASA inside interface IP as default gateway for the clients
ciscoasa(config)# dhcprelay setroute inside

Usage Guidelines

You can add up to four DHCP relay servers per interface. You must add at least one dhcprelay server command to the ASA Firewall configuration before you can enter the dhcprelay enable command. You cannot configure a DHCP client on an interface that has a DHCP relay server configured.

You cannot enable DHCP relay under the following conditions:
• You cannot enable DHCP relay and the DHCP relay server on the same interface.
• You cannot enable DCHP relay and a DHCP server (dhcpd enable) on the same interface.

This article describes the user interface and access modes and commands associated with the operation of Cisco ASA 5500 firewall appliances. We assume that you know how to connect to the appliance using a console cable (the blue flat cable with RJ-45 on one end, and DB-9 Serial on the other end) and a Terminal Emulation software (e.g HyperTerminal), and how to use basic Command Line Interface.

A Cisco ASA security appliance has four main administrative access modes:

Monitor Mode: Displays the monitor> prompt. A special mode that enables you to update the image over the network or to perform password recovery. While in the monitor mode, you can enter commands to specify the location of a TFTP server and the location of the software image or password recovery binary image file to download. You access this mode by pressing the “Break” or “ESC” keys immediately after powering up the appliance.
Unprivileged Mode: Displays the > prompt. Available when you first access the appliance. If the appliance is a Cisco PIX 500 series, the prompt for unprivileged mode is pixfirewall> and if the appliance is the new Cisco ASA 5500 Series, the prompt is ciscoasa>

This mode provides restricted view of the security appliance. You cannot configure anything from this mode. To get started with configuration, the first command you need to know is the enable command. Type enable and hit Enter. The initial password is empty, so hit Enter again to move on the next access mode (Privileged Mode).

ciscoasa> enable <–Unprivileged Mode
password: <– Enter a password here (initially its blank)
ciscoasa# <– Privileged Mode

Privileged Mode: Displays the # prompt. Enables you to change the current settings. Any unprivileged command also works in this mode. From this mode you can see the current configuration by using “show running-config”. Still, you cannot configure anything yet until you go to Configuration Mode. You access the Configuration Mode using the configure terminal command from the Privileged Mode.

Configuration Mode: This mode displays the (config)# prompt. Enables you to change all system configuration settings. Use exit from each mode to return to the previous mode.

ciscoasa> enable <– Unprivileged Mode
password: <– Enter a password here (initially its blank)
ciscoasa# configure terminal <– Privileged Mode
ciscoasa(config)# <– Configuration Mode
ciscoasa(config)# exit
ciscoasa# exit <– Back to Privileged Mode
ciscoasa> <– Back to Unprivileged Mode

The (config)# mode is sometimes called Global Configuration Mode. Some configuration commands from this mode enter a command-specific mode and the prompt changes accordingly. For example the interface command enters interface configuration mode as shown below:

ciscoasa(config)# interface GigabitEthernet0/1
ciscoasa(config-if)# <– Configure Interface specific parameters

Traditionally, a network firewall is a routed hop that acts as a default gateway for hosts that connect to one of its screened subnets. A transparent firewall (or Layer 2 firewall), on the other hand, acts like a “stealth firewall” and is not seen as a Layer 3 hop to connected devices. The appliance connects the same Layer 3 network subnet on its inside and outside ports, but each interface of the firewall resides in a different Layer 2 Vlan. The Cisco ASA firewall can operate both in Routed Firewall Mode (default mode) or in Transparent Firewall Mode.

Routed Firewall Mode:

See the diagram below for a common network topology of a Cisco ASA firewall working in Routed Mode.

As you can see, there are two different network subnets. Inside network ( and Outside Network ( There must be also two different layer2 vlans (Vlan20 for inside network and Vlan10 for outside network). All hosts residing in internal network must belong to subnet and must have default gateway the internal IP of the ASA (

Transparent Firewall Mode:

The diagram below shows an example topology using a Cisco ASA in Layer 2 transparent mode.

As you can see, there is only one Layer 3 network ( BUT there MUST be two different Layer 2 Vlans (Vlan20 for inside zone and Vlan10 for outside zone). All hosts must reside in network range and the devices must have as default gateway the IP address of the outside router ( Also, a management IP address MUST be configured on the ASA firewall (again within the range of DO NOT specify the management IP address of the ASA as the default gateway for connected devices.


Characteristics of Transparent Mode

• Transparent firewall mode supports only two interfaces (inside and outside)
• The firewall bridges packets from one VLAN to the other instead of routing them.
• MAC lookups are performed instead of routing table lookups.
• Can run in single firewall context or in multiple firewall contexts.
• A management IP address is required on the ASA.
• The management IP address must be in the same subnet as the connected network.
• Each interface of the ASA must be a different VLAN interface.
• Even though the appliance acts as a Layer 2 bridge, Layer 3 traffic cannot pass through the security appliance from a lower security level to a higher security level interface.
• The firewall can allow any traffic through by using normal extended Access Control Lists (ACL).

Initial Configuration

Asa(config)# firewall transparent

!Configure management IP below
Asa(config)# ip address

Asa(config)# interface Ethernet0/0
Asa(config-if)# nameif outside
Asa(config-if)# security-level 0
Asa(config)# interface Ethernet0/1
Asa(config-if)# nameif inside
Asa(config-if)# security-level 100

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