A vulnerability in the IPv4 access control list (ACL) feature and quality of service (QoS) policy feature of Cisco IOS XR Software for Cisco ASR 9000 Series Aggregation Services Routers, ASR 9902 Compact High-Performance Routers, and ASR 9903 Compact High-Performance Routers could allow an unauthenticated, remote attacker to cause a line card to reset, resulting in a denial of service (DoS) condition.
This vulnerability is due to the incorrect handling of malformed IPv4 packets that are received on line cards where the interface has either an IPv4 ACL or QoS policy applied. An attacker could exploit this vulnerability by sending crafted IPv4 packets through an affected device. A successful exploit could allow the attacker to cause network processor errors, resulting in a reset or shutdown of the network process. Traffic over that line card would be lost while the line card reloads. Note: This vulnerability has predominantly been observed in Layer 2 VPN (L2VPN) environments where an IPv4 ACL or QoS policy has been applied to the bridge virtual interface. Layer 3 configurations where the interface has either an IPv4 ACL or QoS policy applied are also affected, though the vulnerability has not been observed.
| Software | From | Fixed in |
|---|---|---|
| cisco / ios_xr | 6.7.2 | 6.7.2.x |
| cisco / ios_xr | 6.7.3 | 6.7.3.x |
| cisco / ios_xr | 6.7.35 | 6.7.35.x |
| cisco / ios_xr | 6.8.1 | 6.8.1.x |
| cisco / ios_xr | 6.8.2 | 6.8.2.x |
| cisco / ios_xr | 6.9.1 | 6.9.1.x |
| cisco / ios_xr | 6.9.2 | 6.9.2.x |
| cisco / ios_xr | 7.1.2 | 7.1.2.x |
| cisco / ios_xr | 7.1.3 | 7.1.3.x |
| cisco / ios_xr | 7.1.15 | 7.1.15.x |
| cisco / ios_xr | 7.1.25 | 7.1.25.x |
| cisco / ios_xr | 7.3.1 | 7.3.1.x |
| cisco / ios_xr | 7.3.2 | 7.3.2.x |
| cisco / ios_xr | 7.3.3 | 7.3.3.x |
| cisco / ios_xr | 7.3.4 | 7.3.4.x |
| cisco / ios_xr | 7.3.5 | 7.3.5.x |
| cisco / ios_xr | 7.4.1 | 7.4.1.x |
| cisco / ios_xr | 7.4.2 | 7.4.2.x |
| cisco / ios_xr | 7.5.1 | 7.5.1.x |
| cisco / ios_xr | 7.5.2 | 7.5.2.x |
| cisco / ios_xr | 7.5.3 | 7.5.3.x |
| cisco / ios_xr | 7.5.4 | 7.5.4.x |
| cisco / ios_xr | 7.5.5 | 7.5.5.x |
| cisco / ios_xr | 7.6.1 | 7.6.1.x |
| cisco / ios_xr | 7.6.2 | 7.6.2.x |
| cisco / ios_xr | 7.7.1 | 7.7.1.x |
| cisco / ios_xr | 7.7.2 | 7.7.2.x |
| cisco / ios_xr | 7.8.1 | 7.8.1.x |
| cisco / ios_xr | 7.8.2 | 7.8.2.x |
| cisco / ios_xr | 7.8.22 | 7.8.22.x |
| cisco / ios_xr | 7.8.23 | 7.8.23.x |
| cisco / ios_xr | 7.9.1 | 7.9.1.x |
| cisco / ios_xr | 7.9.2 | 7.9.2.x |
| cisco / ios_xr | 7.10.1 | 7.10.1.x |
A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.
CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.
A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.
Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.
Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.
SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.