A vulnerability in the handling of an Egress Packet Network Interface (EPNI) Aligner interrupt in Cisco IOS XR Software for Cisco Network Convergence System (NCS) 5500 Series with NC57 line cards and Cisco NCS 5700 Routers could allow an unauthenticated, remote attacker to cause the network processing unit (NPU) and ASIC to stop processing, preventing traffic from traversing the interface. This vulnerability is due to the corruption of packets in specific cases when an EPNI Aligner interrupt is triggered while an affected device is experiencing heavy transit traffic.
An attacker could exploit this vulnerability by sending a continuous flow of crafted packets to an interface of the affected device. A successful exploit could allow the attacker to cause persistent, heavy packet loss, resulting in a denial of service (DoS) condition. Cisco has assigned this security advisory a Security Impact Rating (SIR) of High rather than Medium as the score indicates, due to the critical nature of the device's operational environment.
Organizations should prioritize patching immediately to mitigate the risk associated with this vulnerability. If active exploitation of this vulnerability is suspected, contact the Cisco Technical Assistance Center (TAC) or your contracted maintenance provider.
This vulnerability has a CVSS score of 6.8, categorized as Medium severity. The urgency for defenders is high, given the potential for significant disruption within critical network segments.
Vulnerability Details
The vulnerability in question allows the network processing unit (NPU) and application-specific integrated circuit (ASIC) to become unresponsive, which can prevent the normal flow of network traffic. The affected products include Cisco NCS 5500 Series devices and Cisco NCS 5700 Routers running Cisco IOS XR Software. The vulnerability was published on March 11, 2026.
The vulnerability is classified under CWE-460, which refers to the 'Insecure Schema' that can lead to unexpected operational states. The CVSS score of 6.8 reflects a high availability impact, with the attack vector being network-based.
Technical Analysis
The root cause of this vulnerability lies in the handling of interrupts within the EPNI subsystem, specifically when under heavy transit traffic conditions. The attack vector is network-based, and the complexity of the attack is deemed high, requiring no privileges or user interaction.
Successful exploitation leads to high availability impact, causing denial of service. The attacker must send a continuous flow of crafted packets to trigger this state, resulting in significant packet loss.
Risk & Impact Analysis
Organizations using Cisco NCS devices must recognize the operational impact of this vulnerability. Given that these devices often handle critical network functions, a successful attack could lead to severe disruptions and potential data exposure.
The current CVSS score of 6.8 indicates a medium severity, but the context of its operation in critical segments elevates the risk significantly. Organizations should assess their network architecture and implement mitigation strategies promptly.
Exploitation Status
Signal | Status |
|---|---|
Known Exploit | No |
Public PoC | No |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
This vulnerability affects Cisco IOS XR Software for the Cisco Network Convergence System (NCS) 5500 Series with NC57 line cards and Cisco NCS 5700 Routers. All versions prior to vendor patch are affected.
Mitigation & Remediation
Organizations should prioritize patching immediately. Cisco has released patches to address this vulnerability, and it is critical to implement these updates as soon as possible to prevent exploitation. For additional security, organizations may consider implementing network controls to limit the exposure of affected devices.
For continuous validation of security postures, organizations should engage in continuous penetration testing to identify similar vulnerabilities proactively.
Detection Guidance
Monitoring network traffic for unusual patterns and packet loss can help detect potential exploitation attempts. Additionally, logging indicators related to EPNI operations may assist in identifying abnormal behavior indicative of this vulnerability being targeted.
AppSecure Threat Intelligence Insight
The long-term significance of this vulnerability lies in its potential to disrupt critical network operations. Organizations should be aware of the patterns of exploitation associated with similar vulnerabilities in network devices. This incident highlights the importance of proactive measures in vulnerability management and incident response.
As the threat landscape evolves, security teams must remain vigilant and adopt a robust penetration testing methodology to ensure their defenses are resilient against emerging threats.
Moreover, organizations can enhance their security posture by investing in vulnerability management programs that are tailored to their specific operational risks and challenges.
Ultimately, understanding the implications of vulnerabilities like CVE-2026-20118 is crucial for maintaining the integrity and availability of network services.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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