???: David Perry (MKT-US)
????: 2010?3?29? ?? 12:02:29
??: ::NEWSBANK:: Can you trust your network card?
Can you still trust your network card ?
24 March 2010
During the CanSecWest international conference in Vancouver, members of ANSSI (French Network and Information Security Agency) described how an attacker could remotely take full control of a particular network card model.
This page gives a summary of the materials that have been presented and aims at answering questions corresponding to this presentation.
The presentation was entitled “Can you still trust your network card?”. The talk explained how an attacker could be able to exploit a flaw to run arbitrary code inside some network controllers (NICs). The attack uses routable packets delivered to the victim’s NIC. Consequently, multiple attacks can be conducted including: Man in The Middle attacks on network connections, access to cryptographic keys on the host platform, or malware injection on the victim’s computer host platform (see § 2).
The presentation included a description of the flaw as well as a demo of the exploitation possibilities. The tools used for the demo, as well as the proof of concept code were not released during the conference, and will never be.
The slides used for the presentation are available here.
2. An unauthenticated remote attack on a network card! Is it as dangerous as it seems to be?
An unauthenticated remote attack on a network card is almost the most efficient attack one can imagine. A remote attacker located anywhere on the network can take full control of the victim’s network in order to: intercept all packets sent to and from the victim’s machine and forwards them to an attacker on the network; perform man in the middle on all unauthenticated network connexion (such as ARP or DNS) to redirect traffic to target machines; remotely shutdown, reset or wake up the machine.
Moreover, if no IOMMU is used (see below), the attacker can gain access to the victim’s computer memory and take full control of the machine.
However, the attack presented only applies to a specific network card model (Broadcom NetXtreme) whenever a remote administration functionality (called ASF for Alert Standard Format 2.0) is turned on (it is off by default) and configured. According to vendors, this functionality is far from being widely used. As a consequence, this vulnerability is really likely to have a very limited impact in practice. The vendors issued a patch for this vulnerability (see § 5).
3. Is there a proof of concept?
Yes. A proof of concept attack has been demoed during the CanSecWest conference. It showed how an attacker can remotely shutdown or wake up his victim’s machine, and fully compromise a COTS operating system machine (Linux for the demo, but all operating systems are vulnerable).
Please note however that the tools used for the demo, the proof of concept code and network packets were not provided during the conference and will not be released.
4. How can I find out if my machine is vulnerable?
Any computer using Broadcom NetXtreme chips with ASF activated and configured is vulnerable. Users of such computers should apply the official patches (see § 6). Other vendor cards and other cards models are not impacted by this vulnerability. Machines using Broadcom NetXtreme chips when ASF has never been configured (Requires to launch the Broadcom ASF configuration tool) are not vulnerable but patching is highly recommended.
Readers are also advised to follow CERT advisories, e.g CERTA-2010-AVI-121
5. How can I protect my computers from such an attack?
If your computer is vulnerable to this attack you can either (in order of preference):
- apply the vendor patch (see § 6) ;
- deactivate ASF. This should be done using the Broadcom ASF Configuration tool and not by turning off ASF in the BIOS of the machine;
- configure all your network packet-filters to filter UDP ports used by ASF (623 and 664).
Please note that some operating systems actually deactivate ASF at boot time. Some operating systems or hypervisors might also take advantage of hardware technologies such as Intel Vt-d and AMD I/OMMUs that would limit the impact of the attack.
6. Where can I find the patch correcting the flaw?
Patches are provided by OEMs in firmware updates for the NICs.
7. What is the purpose of publishing this in an international conference?
Our goal is to raise awareness on the security problems related to hardware vulnerabilities. We believe that this kind of publication should lead to an improvement of the quality of low level embedded firmware. So far, no research was performed on network card vulnerabilities.
8.Who might be able to carry a similar attack?
Carrying out an attack similar to the one we presented requires:
to identify a flaw in a NIC embedded firmware;
to get sufficient knowledge of the hardware;
to develop tools to identify if and how the flaw will be exploitable;
to craft the correct attack packets and make the exploit stable on a non standard architecture.
We do not expect to see many of these attacks around in the next few months of years, but we proved that carrying out such attacks was possible in practice.
9. Are there other risks related to hardware vulnerabilities?
Hardware components (CPUs, chipsets, graphic adapters, NICs; USB and PCI devices) generally run embedded software (firmware). Flaws in low level firmwares could be exploited by attackers for “rootkit” concealment or privilege escalation purposes.
10. What is the French government doing to improve the things as they are now?
ANSSI has been repeatedly raising awareness in scientific and technical conferences about the attack vectors related to hardware components. ANSSI have been talking to hardware vendors to explain why they should care about security of their hardware and embedded firmware design.
The ANSSI was established by a decree issued in the Journal Officiel de la République Française of July 8th, 2009. The creation of the French Network and Information Security Agency is a milestone in the process of improving France’s capability to protect its sensitive information systems.
The core missions of the new agency are:
To detect and early react to cyber attacks, thanks to the creation of a strong operational center for cyber defence, working round-the-clock and being in charge of the continuous surveillance of sensitive Governmental networks, as well as the implementation of appropriate defence mechanisms;
To prevent threats by supporting the development of trusted products and services for Governmental entities and economic actors;
To provide reliable advice and support to Governmental entities and operators of Critical Infrastructure;
To keep companies and the general public informed about information security threats and the related means of protection through an active communication policy.
ANSSI’s work on trusted computing and low level security
ANSSI’s scientific publication are collected here.
communication [at] ssi.gouv.fr