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Cisco IOS heap integrity checks are insufficient

Vulnerability Note VU#562945

Original Release Date: 2005-11-03 | Last Revised: 2005-11-03


Cisco Internetwork Operating System (IOS) may allow a heap-based buffer overflow vulnerability to execute arbitrary code after bypassing heap integrity checks.


Cisco IOS contains functionality for checking the integrity of the heap, which is a specific region in memory where data is stored. This additional checking ensures that an attacker has not modified the heap through a heap-based buffer overflow vulnerability or other methods.

Nominally, heap integrity checking will force the device to reload if the integrity checks fail. This intended behavior may have the side effect of a temporary denial-of-service condition while the device resets. However, certain conditions have been discovered that may allow an attacker to achieve arbitrary code execution without crashing or resetting the device immediately. In some cases, this may be achieved by overwriting special areas of system memory. The overwritten system memory is then executed in place of the intended system code, resulting in the attacker gaining full control of the device.

This issue is typically coupled with another vulnerability in order to successfully accomplish an entire attack. For example, Cisco IOS may be vulnerable to attacks such as "Cisco IOS vulnerable to DoS or arbitrary code execution via specially crafted IPv6 packet" (VU#930892) due to the heap checker flaw described here being exploited through an entry point established via VU#930892. In other words, the heap integrity checker failure is typically harnessed by other, disparate flaws in order to control the device. By addressing the flaws of the heap integrity checking routines directly, the vulnerability of Cisco IOS to other such flaws is minimized.


An attacker may escalate the impact of another vulnerability in order to take control of the device or execute arbitrary code.


Apply an update
Cisco has addressed this issue in Cisco Security Advisory Document 68064.

Vendor Information


Cisco Systems, Inc. Affected

Updated:  November 03, 2005



Vendor Statement

We have not received a statement from the vendor.

Vendor Information

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


Cisco has addressed this issue in Cisco Security Advisory Document 68064.

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

CVSS Metrics

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Thanks to the Cisco Systems Product Security Incident Response Team for reporting this vulnerability.

This document was written by Ken MacInnis.

Other Information

CVE IDs: None
Severity Metric: 37.80
Date Public: 2005-11-02
Date First Published: 2005-11-03
Date Last Updated: 2005-11-03 18:24 UTC
Document Revision: 10

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