Vulnerability Note VU#178024

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

Original Release date: 25 Oct 2001 | Last revised: 25 Oct 2001


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:


Systems Affected (Learn More)

VendorStatusDate NotifiedDate Updated
CiscoAffected-25 Oct 2001
If you are a vendor and your product is affected, let us know.

CVSS Metrics (Learn More)

Group Score Vector
Base N/A N/A
Temporal N/A N/A
Environmental N/A N/A



Thanks to Cisco Systems for reporting this vulnerability.

This document was written by Shawn Van Ittersum.

Other Information

  • CVE IDs: CAN-2001-0750
  • Date Public: 24 May 2001
  • Date First Published: 25 Oct 2001
  • Date Last Updated: 25 Oct 2001
  • Severity Metric: 11.81
  • Document Revision: 11


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