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CERT Coordination Center

Cisco IOS vulnerable to deferred DoS via SYN scan to certain TCP port ranges

Vulnerability Note VU#178024

Original Release Date: 2001-10-25 | Last Revised: 2001-10-25


Cisco Internetwork Operating System (IOS) may reload unexpectedly after being scanned on certain ports.


Certain versions of Cisco IOS contain a vulnerability that allows the router to enter an unstable state after receiving a connection attempt on any TCP port in the following ranges: 3100-3999, 5100-5999, 7100-7999, and 10100-10999. In this state, the router will reload at the next execution of "show running-config," "write memory," or any command that causes the configuration file to be accessed.


Attackers may cause Cisco routers to reload and cause a denial of service.


Review Cisco Systems's security advisory to determine which versions of IOS are vulnerable and which version you should obtain to eliminate this vulnerability. The advisory is available at:


Vendor Information

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Updated:  October 25, 2001



Vendor Statement

See the information in

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.


The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us email.

CVSS Metrics

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Thanks to Cisco Systems for reporting this vulnerability.

This document was written by Shawn Van Ittersum.

Other Information

CVE IDs: CVE-2001-0750
Severity Metric: 11.81
Date Public: 2001-05-24
Date First Published: 2001-10-25
Date Last Updated: 2001-10-25 23:44 UTC
Document Revision: 11

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