Cisco Security Advisory-
This notice addresses two unrelated security vulnerabilities in the software used on the Cisco 7xx series of small-office and home-office routers. These vulnerabilities affect only the 7xx series routers (not the 7xxx series); no other Cisco product is affected.
The first vulnerability, which has been assigned Cisco bug ID CSCdm03231, can be used to cause system reloads, and therefore denial of service, using TCP connections to the routers' TELNET ports.
The second vulnerability has not been assigned a bug ID. 7xx routers running software versions 3.2(5) through 4.2(3) support a simple HTTP server. This HTTP server is enabled by default. Unless the server is explicitly disabled, it can be used to make changes to the router configuration, and/or to gain information about that configuration. This is intentional behavior, but is mentioned in this notice because it appears that customers have been caught unawares by it.
There are configuration workarounds for both of these vulnerabilities.
This advisory is posted at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-19990311-xxconn.
-
This section provides details on affected products.
Vulnerable Products
Only networks incorporating 7xx series small-office/home-office routers are affected by these vulnerabilities. 7xx routers are designed to provide network connectivity for small remote networks using ISDN BRI lines. If your network includes 7xx series routers, they are most likely to be found in the homes of network users, or in remote offices with no more than a few employees.
CSCdm03231 affects all Cisco 7xx routers, running any software version up to and including release 4.2(3), whose administrators have not taken specific steps to filter incoming TCP connections. Such filtering is not enabled by default.
The HTTP server is present in all software releases from 3.2(5) through 4.2(3), inclusive. The server is enabled by default in all of these software versions.
Products Confirmed Not Vulnerable
Routers running release 4.3(1) or later software are not affected by CSCdm03231.
No other Cisco products are currently known to be affected by these vulnerabilities.
-
CSCdm03231 affects all software versions earlier than 4.3(1). Customers with 76x or 77x routers should upgrade to release 4.3(1). Because of memory limitations, release 4.3 is not supported on the 75x routers; customers with 75x routers should use IP filtering as described in the "Workarounds" section.
The HTTP server is present in all software versions from 3.2(5) through 4.2(3). It is not present in 3.2(4) or earlier releases, nor is it present in 4.3. Customers with 76x or 77x routers should upgrade to release 4.3(1), primarily because of the desirability of installing the CSCdm03231 fix. The HTTP server may be disabled in any software version; disabling the server is the recommended course of action for customers with 75x routers.
-
This section describes workarounds for these vulnerabilities
Workaround for CSCdm03231
CSCdm03231 can be made much less useful to attackers by preventing incoming TCP connections to the router from untrusted hosts. This can be done with the set ip filter profile command, as in the following example:
set ip filter tcp source = not trusted-host destination = router block
This example would configure the router to accept incoming TCP connections only from a single trusted administrative host. More elaborate configurations, permitting connections of various types from various hosts, are possible; see the router documentation for more information.
Disabling the HTTP Server
The HTTP server may be disabled with the system command set clickstart off.
-
When considering software upgrades, also consult http://www.cisco.com/go/psirt and any subsequent advisories to determine exposure and a complete upgrade solution.
In all cases, customers should exercise caution to be certain the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, contact the Cisco Technical Assistance Center ("TAC") or your contracted maintenance provider for assistance.
-
Cisco knows of no public announcements or discussion of CSCdm03231 before the date of this notice. Cisco has had no reports of malicious exploitation of CSCdm03231. CSCdm03231 was found by an outside security company during laboratory testing.
A simple program is needed to effectively exploit CSCdm03231. Although Cisco knows of no program available to the public specifically for this purpose, writing such a program would require very little effort, and only the most basic of skill. Also, certain publicly-available programs intended for other purposes could be used or adapted to exploit the vulnerability.
Cisco has had no reports of abuse of the HTTP server on the 7xx series. However, the potential for abuse is discussed in the product documentation, and must be considered to be known to potential attackers.
-
To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
-
THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.
A stand-alone copy or paraphrase of the text of this document that omits the distribution URL is an uncontrolled copy, and may lack important information or contain factual errors. The information in this document is intended for end-users of Cisco products.