[ISN] Crackers exploit Cisco LAN switch flaw

From: InfoSec News (isnat_private)
Date: Fri Feb 01 2002 - 03:00:47 PST

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    By John Leyden
    Posted: 31/01/2002 at 13:40 GMT
    Cisco has warned users of a potential denial of service risk involving
    its popular Catalyst LAN switches.
    A buffer overflow vulnerability in Telnet option handling can be used
    to crash the process and force a Catalyst switch to reload. This
    operation could be repeated by an attacker to produce a denial of
    service attack.
    Cisco Catalyst switches, series 4000, 5000 and 6000 and also 2948G and
    2900 models, running CatOS are affected by the flaw, which Cisco warns
    has already been exploited. Other Cisco LAN switches and routers are
    The networking giant is offering free software upgrades to affected by
    the flaw and published a schedule for the availability of fixed
    releases, which shows fixes will be available by February 4.
    Cisco is advising users to upgrade software on affected switches as
    soon as is becomes available. In the meantime, workarounds to prevent
    attacks, such as using SSH instead of Telnet, or applying access
    control lists (ACLs) on routers and firewalls in front of vulnerable
    boxes, can be applied.
    The Catalysts switch vulnerability is related to a flaw involving
    systems running versions of telnetd derived from BSD source, which was
    discovered in July last year. At the time this problem was thought to
    relate mainly to Unix systems, but it is now clear it also affects LAN
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