CVE-2015-4199: Race condition in the IPv6-to-IPv4 functionality in Cisco IOS 15.3S in the Performance Routing Engine (PRE)...

Security readout for executives and security teams

CVE-2015-4199 is a Cisco IOS denial-of-service issue affecting UBR devices with PRE modules. Under specific IPv6-to-IPv4 conditions involving many IPv6 CPE devices, a remote attacker may cause a module crash, disrupting service. The source bundle does not provide a CVSS score or confirmed active exploitation. Exposure appears limited to organizations operating Cisco UBR devices with PRE modules running Cisco IOS 15.3S and using the affected IPv6-to-IPv4 functionality. The supplied data does not identify broader products, versions, or CPEs. Treat this as a targeted availability risk for affected Cisco UBR infrastructure. Prioritize if these devices support customer-facing or critical connectivity. If the environment does not use the named Cisco IOS, UBR, and PRE combination, business urgency is lower. Mitigation focus: Review the Cisco advisory for fixed IOS releases or vendor workarounds.; Inventory UBR devices running Cisco IOS 15.3S with PRE modules.; Prioritize maintenance for affected UBR infrastructure supporting IPv6 CPE connectivity..

Prepared

Jun 13, 2026, 22:22 UTC (UTC+00:00)

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.