Software Engineering Institute

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.