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Multiple vulnerabilities have been identified and fixed in CBOS, an operating system for the Cisco 600 family of routers. The following is a list of vulnerabilities that are address by this advisory:
1. Any router in the Cisco 600 family that is configured to allow Web access can be locked by sending a specific URL. Web access is disabled by default, and it is usually enabled in order to facilitate remote configuration. This defect is documented as Cisco bug ID CSCdr98772.
2. By sending a stream of TCP SYN packets to the router, it is possible to exhaust all available TCP sockets. The consequence is that no new TCP sessions addressed to the router will be established. The difference between this vulnerability and a SYN Denial-of-Service attack is that this one can be accomplished by a slow stream of packets (one per second). This defect is documented as Cisco bug ID CSCds59206.
3. Invalid login attempts using the Web interface are not logged. This defect is documented as Cisco bug ID CSCds19142.
4. It is possible to lock up the router by sending a large ICMP ECHO (PING) packet to it. This defect is documented as Cisco bug ID CSCds23921. |
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Credit:
This advisory is also available at: http://www.cisco.com/warp/public/707/CBOS-multiple.shtml .
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Vulnerable systems:
The following releases of CBOS are vulnerable to all defects: 2.0.1, 2.1.0, 2.1.0a, 2.2.0, 2.2.1, 2.2.1a, 2.3, 2.3.2, 2.3.5, 2.3.7 and 2.3.8.
Immune systems:
These defects will be fixed in the following CBOS releases: 2.3.5.015, 2.3.7.002, 2.3.9 and 2.4.1.
Solution:
Customers are urged to upgrade to releases that are not vulnerable to this defect as shown in detail in the section Software Versions and Fixes below.
Affected Products:
The affected models are: 627, 633, 673, 675, 675E, 677, 677i and 678.
These models are vulnerable if they run any of the following, or earlier, CBOS releases: 2.0.1, 2.1.0, 2.1.0a, 2.2.0, 2.2.1, 2.2.1a, 2.3, 2.3.2, 2.3.5, 2.3.7 and 2.3.8.
No other releases of CBOS software are affected by this vulnerability.
No other Cisco products are affected by this vulnerability.
These defects will be fixed in the following CBOS releases: 2.3.5.015, 2.3.7.002, 2.3.9 and 2.4.1
Details:
CSCdr98772
Inadequate URL parsing in CBOS causes the behavior. Each URL was expected to terminate with a minimum of a single space character (ACSII code 32, decimal). Sending a URL that does not terminate with a space causes CBOS to enter an infinite loop.
It is necessary to power cycle the router to resume operation.
In order to exploit this vulnerability, a router must be configured to accept Web connections. Having a Web access password configured does not provide protection against this vulnerability.
Note:
Web access on all Cisco 600 routers is disabled by default and must be explicitly enabled.
Impact:
By sending a tailored URL to a router, it is possible to cause a Denial-of-Service. Every affected router must be powered off and back on in order to restore its normal functionality.
CSCds59206
By sending a stream of SYN packets addressed to the router, it is possible to exhaust all available TCP sockets within CBOS.
This is due to the memory leak in CBOS. When a router is set into a state where it cannot accept a new connection, it can be maintained in this state by a slow stream of SYN packets until the router is rebooted. The stream can be as slow as one packet per second, so one machine with a 64Kb connection can hold up approximately 150 routers.
Note:
This does not affect non-TCP traffic. All User Datagram Protocol (UDP) and Internet Control Message Protocol (ICMP) packets can be handled by a router without any problems. All existing and new TCP sessions through the router will not be affected.
When an attacking stream is terminated, a router recovers itself within a few minutes.
Impact:
It is possible to prevent all TCP access to a router. This blocks all attempts at remote router administration.
CSCds19142
Using the Cisco Web Management interface, it is possible to keep guessing an access password without those password attempts being logged. A password may be either "exec-only" or "enable". A user with an "exec-only" password cannot change a router configuration.
Impact:
In the long term, brute force password guessing can be performed without being noticed. When the correct password is guessed, it can be used to view or modify router configuration. This may be particularly dangerous in installations where multiple routers have the same password.
CSCds23921
By sending a large (at least 65500 bytes in size) ICMP ECHO (PING) packet to the router itself, it is possible to overflow an internal variable and cause router lockup. The packets that are routed through it do not affect the router.
Impact:
It is possible to lock up the router thus causing Denial-of-Service. Every affected device must be powered off and back on in order to restore its normal functionality.
Obtaining Fixed Software
Cisco is offering free software upgrades to eliminate this vulnerability for all affected customers.
Customers with contracts should obtain upgraded software through their regular update channels. For most customers, this means that upgrades should be obtained through the Software Center on Cisco's Worldwide Web site at http://www.cisco.com.
Workarounds:
CSCdr98772
There are two workarounds for this vulnerability. Ensuring that Web access to the router is limited to a legitimate IP address can lessen the potential for exploitation.
This can be done by entering the following commands while in enable mode:
cbos# set web remote 10.0.0.1
cbos# set web remote enabled
Where 10.0.0.1 is the address of the host with a legitimate need for Web access to the router.
Alternatively, disabling the Web access completely will also prevent this vulnerability from being exploited. This can be done by entering the following command while in enable mode:
cbos# set web remote disable
CSCds59206
There is no workaround for this vulnerability.
CSCds19142
The Web Management interface can be disabled by entering the following commands in enable mode:
cbos# set web remote disable
CSCds23921
All incoming ICMP ECHO (PING) packets destined to the router itself should be denied. That can be achieved by following commands:
cbos# set filter number on deny incoming all 0.0.0.0 0.0.0.0 <eth0_IP_address> 255.255.255.255 protocol ICMP
cbos# set filter number+1 on deny incoming all 0.0.0.0 0.0.0.0 <wan0_IP_address> 255.255.255.255 protocol ICMP
Where number is a free filter number between 0 and 17.
Exploitation and Public Announcements
Several customers discovered the vulnerability CSCdr98772. It was also discussed at public forums. PSIRT has received reports that this vulnerability has been exploited in vivo.
A customer discovered the vulnerability CSCds23921. The other two vulnerabilities (CSCds59206 and CSCds19142) were discovered during internal testing.
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