A vulnerability in the implementation of the virtual fragmentation reassembly (VFR) feature for IP version 6 (IPv6) in Cisco IOS Software could allow an
unauthenticated, remote attacker to cause an affected device to hang or reload, resulting in a denial of service (DoS) condition.
vulnerability is due to a race condition while accessing the reassembly
queue for IPv6 fragments. An attacker could exploit this vulnerability
by sending a crafted stream of valid IPv6 fragments. Repeated
exploitation may result in a sustained DoS condition.
Cisco confirmed the vulnerability in a security advisory and released software updates.
Indicators of Compromise
Cisco devices that are running an affected Cisco IOS Software release are vulnerable when the IPv6 VFR feature has been enabled.
Cisco has published a list of affected Cisco IOS Software releases in the security advisory. The "Vendor Announcements" section of this alert contains a link to the advisory.
The vulnerability is due to a race condition that may occur while accessing the reassembly queue for IPv6 fragments.
An unauthenticated, remote attacker could exploit this vulnerability by sending a crafted stream of valid IPv6 fragments to a targeted device. Processing the fragments could cause an affected device to hang or reload, resulting in a DoS condition. Repeated exploitation may result in a sustained DoS condition.
To exploit this vulnerability, the attacker would need to send a crafted stream of valid IPv6 fragments to the targeted system. To achieve this objective, the attacker may need to access trusted, internal network resources. This access requirement reduces the likelihood of a successful exploit.
Cisco indicates through the CVSS score that functional exploit code exists; however, the code is not known to be publicly available.
Administrators are advised to apply the appropriate updates.
Prevent disruption of communication between devices by reducing the impact of attacks that may directly affect the CPU performance of the individual devices. For control plane hardening best practices, see Cisco Guide to Harden Cisco IOS Devices.
Cisco customers with active contracts can obtain updates through the Software Center at the following link: Cisco. Cisco customers without contracts can obtain upgrades by contacting the Cisco Technical Assistance Center at 1-800-553-2447 or 1-408-526-7209 or via email at email@example.com.
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Cisco Multivendor Vulnerability Alerts respond to vulnerabilities identified in third-party vendors' products. These alerts contain information compiled from diverse sources and provide comprehensive technical descriptions, objective analytical assessments, workarounds and practical safeguards, and links to vendor advisories and patches.