CVE-2026-20118 Cisco IOS-XR NCS 5500 and NCS 5700 Egress Packet Network Interfaces Aligner Interrupt Denial of Service Vulnerability
Remote attackers can cause persistent packet loss and denial of service on Cisco NCS routers by sending crafted packets during heavy traffic.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-20118?
CVE-2026-20118 is a medium-severity denial of service vulnerability in Cisco IOS XR Software, published on 11 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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 and Cisco IOS XR Software for Third Party Software 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. Note: If active exploitation of this vulnerability is suspected, contact the Cisco Technical Assistance Center (TAC) or your contracted maintenance provider. Cisco has assigned this security advisory a Security Impact Rating (SIR) of High rather than Medium as the score indicates. This change was made because the affected device operates within a critical network segment where compromise could lead to significant disruption or exposure, thereby elevating the overall risk beyond the base technical severity.
Weakness: CWE-460
Which versions are affected by CVE-2026-20118?
How do I fix CVE-2026-20118?
No fix has been published for CVE-2026-20118 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-20118 being exploited?
There is no known exploitation of CVE-2026-20118 in the wild and no public exploit code.
Sources
Also known as GHSA-vgpf-3m99-q785.