# 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.

- **Severity:** Medium 6.8 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 11 Mar 2026
- **Updated:** 11 Mar 2026
- **Also known as:** GHSA-vgpf-3m99-q785

## 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 (Improper Cleanup on Thrown Exception)

## 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.

## Is CVE-2026-20118 being exploited?

There is no known exploitation of CVE-2026-20118 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-20118 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-20118 in the wild and no public exploit code.

Affected product: Cisco IOS XR Software. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-20118/ (Markdown: https://insights.sbomify.com/CVE-2026-20118/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-20118
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-20118
- OSV: https://osv.dev/vulnerability/CVE-2026-20118

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-20118/
Summaries are generated and may contain mistakes; the official description above is the record.