Cisco Security Advisory-
Cisco 12000 series Gigabit Switch Routers running certain versions of Cisco IOS software forward unauthorized traffic due to an error encountered while processing the established keyword in an access-list statement. The resulting vulnerability could be exploited to circumvent a site's security policy.
Only Cisco Gigabit Switch Routers (currently the 12008 and 12012 GSRs) running Cisco IOS software release 11.2(14)GS2 through 11.2(15)GS3 are vulnerable.
This error is corrected in release 11.2(15)GS5 and later versions.
This error is not present in any version of Cisco IOS software release 12.0S and later. Non-GSR releases are not affected.
The bug ID associated with this error is CSCdm36197.
This advisory is posted at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-19990608-ios-grs-acl.
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This section provides details on affected products.
Vulnerable Products
A GSR running release 11.2(14)GS2 through 11.2(15)GS3 is vulnerable if the keyword established is used in an access-list statement.
The Cisco 12000 series Gigabit Switch Router is a large rack-mount device, approximately twenty to sixty inches (0.5 to 1.5meters) tall and twenty inches (0.5 meters) deep, that requires specialized power connections to supply forty to sixty amps of electricity. GSRs are typically used by major Internet Service Providers at their most important interconnection points. If you do not have a Cisco 12000 series GSR, then you are not affected by the vulnerability described in this notice.
Products Confirmed Not Vulnerable
A GSR running release 11.2(15)GS5 and later or any version of release 12.0S is not affected.
The Cisco 12000 series Gigabit Switch Router (GSR) is the only Cisco product that is affected by this vulnerability. Currently the 12008 GSR and the 12012 GSR are the only two models in the series.
No other Cisco products are currently known to be affected by these vulnerabilities.
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When an affected Cisco Gigabit Switch Router (GSR) executes the following command on an interface:
access-list 101 permit tcp any any established
the established keyword is ignored. This will cause the GSR to forward all TCP traffic for the relevant interface, contrary to the restriction intended in the access-list statement.
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If you need the functionality provided by the established keyword for an access-list command, there is no reasonable workaround.
Customers may wish to consider modifying the policies on other network components, if possible, to limit exploitation of this vulnerability until such time as they have downloaded a fixed version of software to the affected GSR.
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This bug, documented as CSCdm36197, initially appears in 11.2(14)GS2, the first release of Cisco IOS software to support access lists on the GSR.
The bug is present in versions of Cisco IOS software from 11.2(14)GS2 to 11.2(15)GS3, inclusive. The earliest repaired version is 11.2(15)GS5.
If you are running any vulnerable version of 11.2GS and wish to resolve this problem with the least possible change to your existing version of software, you should upgrade to 11.2(15)GS5 or later.
This bug is not present in any release of 12.0S, so upgrading to 12.0S or later will also remove the vulnerability.
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Cisco knows of no public announcements or discussion of this vulnerability before the date of the public release of this notice. No incidents of malicious exploitation of this vulnerability have been reported to Cisco.
This vulnerability was reported to Cisco by a customer.
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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.
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Revision 1.2
1999-June-08
More boilerplate.
Revision 1.1
1999-June-08
Fix boilerplate problems.
Revision 1.0
1999-June-08
Initial public release.
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