Vulnerability Note VU#217912

Cisco IOS fails to properly process TCP packets

Original Release date: 24 Jan 2007 | Last revised: 02 Feb 2007


The Cisco IOS Transmission Control Protocol listener contains a memory leak.


Cisco IOS is an operating system that is used on Cisco network devices. The Cisco IOS software can run Transmission Control Protocol (TCP) servers that allow administrators to connect to the devices for management or monitoring purposes.

A vulnerability exists in the IOS TCP listener. An attacker may be able to craft an IPv4 TCP packet that causes IOS to leak memory when processed. An attacker may be able to exploit this vulnerability to create a denial-of-service condition. The specially crafted TCP can be delivered outside the context of a fully established TCP 3-way handshake.


A remote, unauthenticated attacker with the ability to supply specially crafted TCP packets could cause memory to leak in the affected service. Sustained exploitation could eventually cause a denial of service due to shortage of memory in the affected device and would require a system reset to recover. An attacker could send spoofed TCP packets to trigger this vulnerability making an attack harder to detect or stop.

Note that Cisco states that this vulnerability only applies to traffic destined to the affected device. Traffic transiting the device will not trigger this vulnerability.


See the Software Version and Fixes section of Cisco Security Advisory 200701 for information on available upgrades.

Restrict Access

Restricting public access to TCP servers running on vulnerable systems may mitigate this vulnerability. Access control lists, management VLANs, or alternate connection methods such as modem or console ports can be used to allow restricted access to the device.

Disable Services

Disabling all services that accept incoming TCP connections on a vulnerable device may prevent this vulnerability from being exploited.

For more information about these and other workarounds, see the Workarounds section of Cisco Security Advisory 20070124.

Systems Affected (Learn More)

VendorStatusDate NotifiedDate Updated
Cisco Systems, Inc.Affected-24 Jan 2007
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 for information that was used in this report.

This document was written by Ryan Giobbi.

Other Information

  • CVE IDs: Unknown
  • Date Public: 24 Jan 2007
  • Date First Published: 24 Jan 2007
  • Date Last Updated: 02 Feb 2007
  • Severity Metric: 7.53
  • Document Revision: 39


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