Denial of Service In Cisco IOS Telnet

Reported August 27, 2004, by CiscoSystems

VERSIONS AFFECTED

DESCRIPTION
A Denial of Service (DoS) condition exists in all Cisco IOS-based products thatuse Telnet or reverse Telnet. A specifically crafted TCP connection to a Telnetor reverse Telnet port of a Cisco Systems' device that's running IOS mightblock further Telnet, reverse Telnet, remote shell (Rsh), Secure Shell (SSH),and in some cases HTTP access to the device.

VENDOR RESPONSE
Cisco Systems has releasedSecurity Advisory 61671, "Cisco Telnet Denial of Service Vulnerability,"to address the vulnerability and recommends that affected users immediatelyapply the appropriate patch available via normal update channels.

CREDIT
Discovered by Cisco Systems.