CVE-2018-0157 in IOS XE
Summary
by MITRE
A vulnerability in the Zone-Based Firewall code of Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause a device to reload. The vulnerability is due to the way fragmented packets are handled in the firewall code. An attacker could exploit this vulnerability by sending fragmented IP Version 4 or IP Version 6 packets through an affected device. An exploit could allow the attacker to cause the device to crash, resulting in a denial of service (DoS) condition. The following releases of Cisco IOS XE Software are vulnerable: Everest-16.4.1, Everest-16.4.2, Everest-16.5.1, Everest-16.5.1b, Everest-16.6.1, Everest-16.6.1a. Cisco Bug IDs: CSCvf60296.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 02/06/2021
This vulnerability resides within the Zone-Based Firewall implementation of Cisco IOS XE Software, representing a critical denial of service flaw that can be exploited remotely without authentication. The vulnerability specifically manifests in the handling of fragmented Internet Protocol packets, where the firewall code fails to properly process fragmented IPv4 or IPv6 packets that traverse the affected devices. The root cause lies in the insufficient validation and processing mechanisms within the firewall's packet handling routines, creating a condition where malformed or specially crafted fragmented packets can trigger unexpected behavior in the device's memory management and packet processing modules.
The technical exploitation occurs when an unauthenticated remote attacker crafts and transmits fragmented IP packets through an affected Cisco IOS XE device that has Zone-Based Firewall enabled. When the device processes these fragmented packets, the firewall code encounters a condition that causes the device's memory management subsystem to enter an unstable state, ultimately leading to a system crash and subsequent device reload. This behavior represents a classic buffer over-read or improper input validation vulnerability that can be triggered by malformed packet fragments, where the device's response to these packets results in an uncontrolled termination of the firewall service or the entire operating system.
The operational impact of this vulnerability extends beyond simple service disruption as it can be leveraged to create sustained denial of service conditions against network infrastructure. Network administrators face the challenge of maintaining availability for critical network services, as an attacker can repeatedly exploit this vulnerability to force device reboots, potentially causing cascading failures in network topology and disrupting business operations. The vulnerability affects multiple releases within the Everest branch of Cisco IOS XE Software, specifically versions 16.4.1, 16.4.2, 16.5.1, 16.5.1b, 16.6.1, and 16.6.1a, indicating a widespread issue across several software releases that were likely deployed in production environments. The vulnerability's classification aligns with CWE-129, which addresses insufficient input validation, and can be mapped to ATT&CK technique T1499.004 for network disruption and system resource compromise.
Cisco has identified this issue through internal bug tracking systems and assigned the identifier CSCvf60296 to monitor the vulnerability's remediation process. The vulnerability demonstrates the importance of proper packet fragmentation handling in network security devices, as fragmented packets represent a legitimate network communication mechanism that must be processed safely without introducing instability. Network security professionals should consider implementing temporary workarounds such as disabling fragmented packet processing, implementing access control lists to filter suspicious traffic patterns, or applying the appropriate software patches as soon as they become available. The vulnerability serves as a reminder of the critical need for robust input validation in network infrastructure software and highlights the potential for remote code execution or system compromise when basic packet handling mechanisms are not properly secured against malformed inputs. Organizations should prioritize patch management processes to ensure immediate deployment of Cisco's security advisories addressing this specific vulnerability in their production network environments.