From VM Wed Apr 11 12:06:36 2001 -----BEGIN PGP SIGNED MESSAGE----- CERT Advisory CA-2001-08 Multiple Vulnerabilities in Alcatel ADSL Modems Original release date: April 10, 2001 Last revised: -- Source: CERT/CC A complete revision history can be found at the end of this file. Systems Affected * Alcatel Speed Touch Home ADSL Modem * Alcatel 1000 ADSL Network Termination Device Overview The San Diego Supercomputer Center (SDSC) has recently discovered several vulnerabilities in the Alcatel Speed Touch Asymmetric Digital Subscriber Line (ADSL) modem. These vulnerabilities are the result of weak authentication and access control policies and exploiting them will lead to one or more of the following: unauthorized access, unauthorized monitoring, information leakage, denial of service, and permanent disability of affected devices. The SDSC has published additional information regarding these vulnerabilities at http://security.sdsc.edu/self-help/alcatel/ I. Description VU#211736 - Alcatel ADSL modems grant unauthenticated TFTP access via Bounce Attacks Alcatel ADSL modems allow unauthenticated Trivial File Transfer Protocol (TFTP) access from the local area network (LAN) as a method to update firmware and to make configuration changes to the device. In conjunction with one of several common vulnerabilities, a remote attacker may be able to gain unauthenticated access as well. For example, if a system on the LAN side of the ADSL modem has the UDP echo service enabled, a remote attacker may be able to spoof packets such that the ADSL modem will believe that this traffic originated from the local network. By sending a packet to the UDP echo service with a spoofed source port of 69 (TFTP) and a source address of 255.255.255.255, the system providing the echo service can be tricked into sending a TFTP packet to the ADSL modem. If a system offering this service is accessible from the Internet it may be possible to use the system to attack the ADSL modem. Any mechanism for "bouncing" UDP packets off systems on the LAN side of the network may potentially allow a remote attacker to gain TFTP access to the device. Gaining TFTP access to the device allows the remote attacker to essentially gain complete control of the device. VU#243592 - Alcatel ADSL modems provide EXPERT administrative account with an easily reversible encrypted password Alcatel ADSL modems contain a special account (EXPERT) for gaining privileged access to the device. This account is secured via a challenge-response password authentication mechanism. While the use of such a mechanism is commendable, the algorithm used is not sufficiently strong. Attackers who know the algorithm used to compute the response can compute the correct response using information given to them during the login process. Because the EXPERT account is accessible via TELNET, HTTP, and FTP, the ADSL modem must have an IP address that is accessible from the Internet to exploit this vulnerability. Alcatel ADSL products do not enable this feature over the wide area network (WAN) interface by default. Note however, that an attacker with TFTP access may be able to reconfigure the device to enable this feature. This authentication mechanism is present even if the user has set a user supplied password. Any problem or vulnerability on your internal network that allows an intruder to communicate with the modem may lead to its compromise, including Trojan horses, compromised systems, or other "bounce" vulnerabilities like the FTP bounce vulnerability described in http://www.cert.org/tech_tips/ftp_port_attacks.html VU#212088 - Alcatel ADSL modems contain a null default password The Alcatel Speed Touch ADSL modem ships with a null default password, permitting unauthenticated access via TELNET, HTTP, and FTP. As with the EXPERT account vulnerability, the device must have an externally accessible IP address. VU#490344 - Alcatel ADSL modems provide unauthenticated TFTP access via physical access to the WAN interface To allow your ISP to upgrade the firmware of the ADSL modem remotely, unauthenticated TFTP access is provided to users with physical access to the wire on the WAN side of the modem. While this access is normally used by your ISP, it could also be abused by an attacker with physical access to the wire outside of your home. II. Impact VU#211736 - Alcatel ADSL modems grant unauthenticated TFTP access via Bounce Attacks A remote attacker may be able to gain access to perform TFTP operations. These operations include * inspection of configuration data * recovery and setting of passwords * inspection and updates to the firmware * destructive updates to the firmware * malicious custom updates to the firmware Note that the Alcatel ADSL modems do not provide any mechanism for determining the validity of firmware updates, so a remote attacker may be able to install custom firmware that operated as a distributed denial of service client or a network sniffer. Similarly, an attacker could produce an invalid firmware revision that would disable the device completely, leaving victims no alternative but to return the disabled unit to the manufacturer. VU#243592 - Alcatel ADSL modems provide EXPERT administrative account with an easily reversible encrypted password Attackers who are able to connect to the ADSL modem can enter a predictable user ID and password to gain privileged access to the device. This access can be used to reconfigure the device, potentially introducing additional security weaknesses. VU#212088 - Alcatel ADSL modems contain a null default password Unless the user or Internet service provider changes the default password of an affected device, a remote attacker can access the modem via TELNET, HTTP, or FTP. In the case of TELNET and HTTP, this vulnerability grants the attacker read and write access to device configuration. For FTP, this vulnerability allows the attacker to browse the file structure of the affected device. VU#490344 - Alcatel ADSL modems provide unauthenticated TFTP access via physical access to the WAN interface An attacker with physical access to your wire may be able to gain unauthenticated TFTP access to the device with the same impacts as described in the "bounce" vulnerability (VU#211736). III. Solution Set a password for your ADSL modem Because the Alcatel ADSL modems ship without a password by default, an attacker may be able to gain access if this password has not been set. Users are encouraged to set a password when the device is first configured. This solution does not protect you from all of the vulnerabilities described above. In particular, a user supplied password does not prevent the use of the EXPERT account. Block malicious traffic at your network perimeter If you have a home firewall product you may be able to prevent the TFTP UDP bounce attack by filtering one or more of the following types of traffic: + packets with spoofed source addresses + packets with a source address of 255.255.255.255 + packets with a destination port of echo (or other "simple" services) Note that intruders who are able to gain access to your local area network may be able to gain unauthenticated TFTP access using mechanisms other than the TFTP UDP bounce method. Appendix A. - Vendor Information This appendix contains information provided by vendors for this advisory. When vendors report new information to the CERT/CC, we update this section and note the changes in our revision history. If a particular vendor is not listed below, we have not received their comments. Alcatel ALCATEL SPEED TOUCH ADSL MODEM SECURITY INFORMATION About security of Modems and Networks Security issues can be divided into two main areas: network security and user security, more particularly user's content security. Wide Area Network (WAN) security is about protecting a network from malicious usage. Security can be guaranteed at all network levels except at Customer Premise Equipment (CPE), since such equipment is not directly controlled by an Operator or an ISP. This is true for any type of CPE, such as telephones, analogue, DSL or cable modems and fax machines. Security can only be guaranteed at the network level for an Operator's, ISP's or private network. This means that a network should stay operational at all times. Alcatel has built this type of security in its DSLAM (operated by the service provider). User security is about protecting the content and local area network of an end-user. This type of security has to be implemented on Local Area Network (LAN) or PC level at customer premises. This is standard practice for any network connection (leased lines, cable modem, DSL). Such modems provide connectivity not security. Security of content for the user can be reinforced at the LAN level by installing a dedicated firewall HW/SW, either on the server or on the PC or by installing a dedicated firewall device, although Alcatel provides also DSL modems which have firewall security Statement. Private and LAN security is in the responsibility of the user. There are many soft and hardware products on the market to ensure security, including those from Alcatel. Modem security Firstly, people have been able to alter firmware on the modem. This is a standard feature foreseen in some of the Speed Touch modems to allow SW upgrades locally or remotely. Access from the LAN interface into the modem is not a security problem, since the modem belongs to the person who is using it. However, via a protection mechanism a feature is foreseen so that nobody can do that remotely (or via the WAN/DSL interface). This protection mechanism guarantees that nobody from outside can access the modem and make changes. This protection can be switched off locally by the modem owner, in case the service provider wants to do upgrades. This process is normally managed by the service provider, and the service provider explains to the end-user how to disactivate the protection and re-activate again. To avoid security problems, this feature is not explained in the user manual. Alcatel ships all modems with the protection activated, however, it's easy for a modem owner to disactivate the protection, since this is documented on the Alcatel website. However, if a user disactivates this, he's also responsible for activating it again. Secondly, the method of getting into the modem is more advanced and it is a standard practice used by hackers. The way it works is that they fake local communication via the WAN interface by using an ECHO port on a UNIX server connected to LAN network. The modem assumes communication comes from the modem owner and is secure. However, this is an old security problem in all data communication networks and is solved by means of a firewall. Firewall's are standard practice for each well managed communication network. Recommendation that Alcatel gives is to install a dedicated firewall or firewall software, or make use of the Alcatel Speed Touch modem with Firewall capabilities. (See URL: http://www.alcatel.com/consumer/dsl/prodprofw.htm) _________________________________________________________________ The CERT Coordination Center would like to thank Tom Perrine and Tsutomu Shimomura of the San Diego Supercomputer Center for notifying us about this problem and their help in constructing this advisory. _________________________________________________________________ Authors: This document is based on research by the SDSC and was written by Cory Cohen, Jeffrey P. Lanza, and John Shaffer. ______________________________________________________________________ This document is available from: http://www.cert.org/advisories/CA-2001-08.html ______________________________________________________________________ CERT/CC Contact Information Email: cert@cert.org Phone: +1 412-268-7090 (24-hour hotline) Fax: +1 412-268-6989 Postal address: CERT Coordination Center Software Engineering Institute Carnegie Mellon University Pittsburgh PA 15213-3890 U.S.A. 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Please include in the body of your message subscribe cert-advisory * "CERT" and "CERT Coordination Center" are registered in the U.S. Patent and Trademark Office. ______________________________________________________________________ NO WARRANTY Any material furnished by Carnegie Mellon University and the Software Engineering Institute is furnished on an "as is" basis. Carnegie Mellon University makes no warranties of any kind, either expressed or implied as to any matter including, but not limited to, warranty of fitness for a particular purpose or merchantability, exclusivity or results obtained from use of the material. Carnegie Mellon University does not make any warranty of any kind with respect to freedom from patent, trademark, or copyright infringement. _________________________________________________________________ Conditions for use, disclaimers, and sponsorship information Copyright 2001 Carnegie Mellon University. Revision History April 10, 2001: Initial release -----BEGIN PGP SIGNATURE----- Version: PGP for Personal Privacy 5.0 Charset: noconv iQCVAwUBOtOWzwYcfu8gsZJZAQH4GQP+MpvNtGJX7r+59NaLZFS/GzT0cW8OzE9A YOrHy1glfgb1WZWjAcuiAqwP+yG4piOwkHfGfvTjIPiM/PrhDt86FjIeblXayS9X On1VruE8hLM4bPFUs9+5Kq6XsMC5Y1hJxegfg0oJVWsb+9Dd0cyU0IYZrjdW7Lww FSIbsHoMWG0= =+4q7 -----END PGP SIGNATURE-----