Cisco Security Advisory-
A series of failed telnet authentication attempts to the switch can cause the Catalyst Switch to fail to pass traffic or accept management connections until the system is rebooted or a power cycle is performed. All types of telnet authentication are affected, including Kerberized telnet, and AAA authentication.
This vulnerability has been assigned Cisco bug ID CSCds66191.
The complete advisory can be viewed at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20001206-catalyst-memleak.
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This section provides details on affected products.
Vulnerable Products
These products are vulnerable:
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Catalyst 4000 and 5000 images running version 4.5(2) up to 5.5(4) and
5.5(4a).
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Catalyst 6000 images running version 5.3(1)CSX, up to and including
5.5(4) and 5.5(4a).
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Versions 6.1(1)b and 6.1(2) were not affected in tests for the
vulnerability; however, the code fixes were included in those releases as a
precautionary measure.
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The Catalyst 5000 series images are installed on the Catalyst 2901,
2902, 2926T, 2926F, 2926GL, 2926GS fixed configuration chassis, and the 5000,
5002, 5500, 5505, and 5509 modular chassis switches.
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The Catalyst 4000 series is installed on the Catalyst 2948G, 2980G,
4003, 4006, and 4912G switches.
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The Catalyst 6000 series is installed on the Catalyst 6009, 6006,
6509, 6509-NEB, and 6506 modular chassis switches.
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The Catalyst 2900XL platform is NOT affected by this vulnerability.
Products Confirmed Not Vulnerable
No other releases of Cisco Catalyst software are affected by this vulnerability. No other Cisco products are currently known to be affected by these vulnerabilities.
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Catalyst 4000 and 5000 images running version 4.5(2) up to 5.5(4) and
5.5(4a).
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The telnet process fails to release resources upon a failed authentication, or a successful login of extremely short duration such as a telnet from within an automated script. This memory leak eventually results in the failure of the switch to perform any other processes, such as forwarding traffic or management; a power cycle or reboot is required for recovery.
The command "show process memory" will indicate increased "Holding" memory after failed telnet authentication attempts. This value will not decrease over time except when a reboot, reload, or power cycle occurs. This bug may be triggered over a period of time in the course of normal operation by legitimate users that occasionally fail authentication.
lt-6509-e> (enable) sh proc mem Memory Used:?? 3974544 ?????? Free:? 15265168 ????? Total:? 19239712 PID??????? TTY??????? Allocated? Freed????? Holding??? Process ---------- ---------- ---------- ---------- ---------- --------------- 1????????? -2???????? 1707632??? 3488?????? 1704144??? Kernel and Idle 24???????? -2???????? 16???????? 0????????? 16???????? telnetd???????
Version 4.5(x) of the Catalyst software does not include the command "show process memory", so you can use the command "show mbuf total" to monitor the memory on the switch. If the "free mbufs" entry decreases and stays low, this indicates a memory leak, which may or may not be related to telnet authentication failures. The Technical Assistance Center can further troubleshoot the device to determine the source of the memory leak if necessary.
Sample Output:
switch> (enable) show mbuf total mbufs 10296 clusters 5280 free mbufs 9756 clfree 4767 lowest free mbufs 4976 lowest clfree 0 switch> (enable)
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There is no configuration workaround to eliminate the problem. However, if you are unable to upgrade to an unaffected version, you may use other devices to strictly control or prohibit telnet access to the switch, permitting only connections from your local network.
Access control lists on the switch can limit the remote exploitation of the vulnerability. To limit access to known hosts use the following commands:
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set ip permit enable
telnet
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set ip permit <addr>
[mask]
Remote management of the switch can also be disabled.
The above workarounds are provided as an option; however, the recommendation is to upgrade to fixed code as soon as possible.
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set ip permit enable
telnet
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Cisco has made the following fixed software available to customers:
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Catalyst Release 4.5(10) for Catalyst 4000 and 5000.
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Catalyst Release 5.5(4b) for Catalyst 4000, 5000 and
6000.
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Catalyst Release 6.1(1)b and 6.1(2) for Catalyst 6000.
The fix will be carried forward into all future releases.
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Catalyst Release 4.5(10) for Catalyst 4000 and 5000.
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Cisco Systems knows of no public discussion nor active exploits involving this vulnerability, which was reported by a customer who noted the memory leak.
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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 1.3
2000-December-20
Updated Affected Products list.
Revision 1.2
2000-December-11
Added details of the "show mbuf total" command, which can be used to monitor memory on the switch in the Details section.
Revision 1.1
2000-December-07
Added information about Catalyst software versions 6.1(1)b and 6.1(2) in the Affected Products and Software Versions and Fixes sections.
Revision 1.0
2000-December-06
Initial public release.
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