CVE-2026-20118
Denial of Service via EPNI Interrupt in Cisco IOS XR
Publication date: 2026-03-11
Last updated on: 2026-03-11
Assigner: Cisco Systems, Inc.
Description
Description
CVSS Scores
EPSS Scores
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| Percentile: |
Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| cisco | ncs_5500 | * |
| cisco | ncs_5700 | 25.2 |
| cisco | ncs_5700 | 25.3 |
| cisco | ncs_5700 | 25.4 |
| cisco | ncs_5700 | 26.1 |
| cisco | ncs_5700 | to 7.10 (exc) |
| cisco | ncs_5700 | to 7.11 (exc) |
| cisco | ncs_5700 | to 24.1 (exc) |
| cisco | ncs_5700 | to 24.4 (inc) |
| cisco | ncs_5700 | to 25.2 (exc) |
| cisco | ncs_5700 | 7.9.2 |
| cisco | ncs_5700 | 7.10.2 |
| cisco | ncs_5700 | 7.11.2 |
| cisco | ncs_5700 | 7.11.21 |
| cisco | ncs_5700 | 24.1.2 |
| cisco | ncs_5700 | 24.2.2 |
| cisco | ncs_5700 | 24.2.21 |
| cisco | ncs_5700 | 24.3.2 |
| cisco | ncs_5700 | 24.4.2 |
| cisco | ncs_5700 | 25.1.2 |
| cisco | ios_xr | * |
| cisco | ncs_5500_series | * |
| cisco | ncs_5700 | * |
| cisco | third_party_software | * |
Helpful Resources
Exploitability
| CWE ID | Description |
|---|---|
| CWE-460 | The product does not clean up its state or incorrectly cleans up its state when an exception is thrown, leading to unexpected state or control flow. |
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?
[{'type': 'paragraph', 'content': 'This vulnerability exists in Cisco IOS XR Software used in Cisco Network Convergence System (NCS) 5500 Series with NC57 line cards, NCS 5700 Routers, and certain third-party hardware. It is caused by improper handling of an Egress Packet Network Interface (EPNI) Aligner interrupt, which can corrupt packets when triggered during heavy transit traffic.'}, {'type': 'paragraph', 'content': "An unauthenticated remote attacker can exploit this by sending a continuous stream of specially crafted packets to an affected device's interface. This causes the network processing unit (NPU) and ASIC to stop processing traffic, leading to persistent heavy packet loss and a denial of service (DoS) condition."}] [1]
How can this vulnerability impact me? :
The vulnerability can cause a denial of service (DoS) condition by stopping the network processing unit and ASIC from processing traffic on affected devices. This results in persistent heavy packet loss and prevents traffic from traversing the interface.
Because the affected devices often operate within critical network segments, exploitation could lead to significant network disruption or exposure, impacting network availability and reliability.
How does this vulnerability affect compliance with common standards and regulations (like GDPR, HIPAA)?:
I don't know
How can this vulnerability be detected on my network or system? Can you suggest some commands?
[{'type': 'paragraph', 'content': 'This vulnerability can be detected by checking for EPNI Aligner interrupts on affected Cisco IOS XR devices.'}, {'type': 'list_item', 'content': 'Use the command: show asic-errors fia all location "" | begin Aligner'}, {'type': 'paragraph', 'content': 'If the output contains "AlignerTransmitSizeAboveThInt", it indicates an interrupt event related to this vulnerability.'}, {'type': 'paragraph', 'content': 'Additionally, verifying affected hardware can be done using the command: show inventory'}] [1]
What immediate steps should I take to mitigate this vulnerability?
There are no workarounds available for this vulnerability.
Cisco strongly recommends upgrading to fixed software releases or applying the provided Software Maintenance Updates (SMUs) to mitigate the issue.
- Upgrade to Cisco IOS XR versions 25.2 and later, 25.3, 25.4, or 26.1.
- For earlier versions such as 7.9, 7.10, 7.11, 24.1 through 24.4, and 25.1, apply the specific SMUs available.
Ensure sufficient device memory and compatibility before upgrading.
If active exploitation is suspected, contact the Cisco Technical Assistance Center (TAC) or your contracted maintenance provider immediately.