Cisco Security Advisory
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CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
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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.
Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.
This advisory is available at the following link:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-xrncs-epni-int-dos-TWMffUsNThis advisory is part of the March 2026 release of the Cisco IOS XR Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: March 2026 Semiannual Cisco IOS XR Software Security Advisory Bundled Publication.
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Vulnerable Products
This vulnerability affects the following Cisco products if they are running a vulnerable release of Cisco IOS XR Software, regardless of the device configuration:
- NCS 5700 Series line cards with the following products IDs (PIDs):
- NC57-18DD-SE
- NC57-24DD
- NC57-36H-SE
- NC57-36H6D-S
- NC57-MOD-S
- NCS 5700 Series Fixed Chassis with the following PIDs:
- NCS-57B1-5D24H-SE
- NCS-57B1-5DSE-SYS
- NCS-57B1-6D24-SYS
- NCS-57B1-6D24H-S
This vulnerability also affects Cisco IOS XR for Third Party Hardware if the third-party hardware has a Jericho 2 ASIC.
For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.
Determine Whether an Affected Line Card Is Installed
To determine if an affected line card is installed on a system, use the show inventory CLI command and look for the PIDs of affected line cards:
RP/0/RP0/CPU0:NCS_Router# show inventory
Tue Feb 18 10:55:15.397 UTC
NAME: "0/0", DESCR: "NCS 5700 18x400GE Line Card with TCAM"
PID: NC57-18DD-SE , VID: V03, SN: JAE271602RT
NAME: "HundredGigE0/0/0/0", DESCR: "Cisco QSFP28 100G SR4 Pluggable Optics Module"
PID: QSFP-100G-SR4-S , VID: V03, SN: INL270701RY
NAME: "FourHundredGigE0/0/0/18", DESCR: "Cisco QSFPDD 400G DR4 Pluggable Optics Module"
PID: QDD-400G-DR4-S , VID: V02 , SN: INL27060SZ7
NAME: "0/1", DESCR: "NCS 5700 36x100GE 6x400GE Line Card"
PID: NC57-36H6D-S , VID: V01, SN: JAE27170FQG
NAME: "0/2", DESCR: "NCS 5700 2XMPA Scaled Line Card, MACSec"
PID: NC55-MOD-A-SE-S , VID: V02, SN: JAE2714041Y
NAME: "GigabitEthernet0/2/0/4", DESCR: "Cisco SFP 1G 1000BASE-SX Pluggable Optics Module"
PID: SFP-GE-S , VID: V01, SN: FNS11510HSN
NAME: "0/3", DESCR: "NCS 5700 36x100GE Line Card with TCAM"
PID: NC57-36H-SE , VID: V02, SN: JAE271406WCProducts Confirmed Not Vulnerable
Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.
Cisco has confirmed that this vulnerability does not affect the following Cisco products:
- IOS Software
- IOS XE Software
- IOS XR Software that is running on devices other than the models listed in the Vulnerable Products section of this advisory
- NX-OS Software
- NCS 5700 Series line cards with the following products IDs (PIDs):
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An EPNI Aligner interrupt on a device may be evidence of an attempted attack using this vulnerability. To check for interrupts, use the show asic-errors fia all location "" | begin Aligner command.
RP/0/RP0/CPU0:NCS_Router# show asic-errors fia all location 0/4/CPU0 | begin Aligner
<Output Snipped>
Name : EPNI_0.Interrupt_Register.AlignerTransmitSizeAboveThInt
Leaf ID : 0x36030011
Error count : 2
Last clearing : DDD MMM X HH:MM:SS YYYY
Last N errors : 2
--------------------------------------------------------------
First N errors.
@Time, Error-Data
------------------------------------------
<Output Snipped>
Error description: Check for misconfiguration in ETPP|None
<Output Snipped>
Error description: Check for misconfiguration in ETPP|NoneIf the output of this command includes AlignerTransmitSizeAboveThInt in the Name field, an EPNI Aligner interrupt has occurred.
However, devices that are running a fixed release of Cisco IOS XR Software or have an SMU installed to address this vulnerability will handle the interrupt gracefully and will not be affected by this vulnerability. If a device is running a vulnerable release of Cisco IOS XR Software, an EPNI Aligner interrupt could result in a DoS condition.
Cisco strongly recommends that all customers who have affected PIDs in their networks install the appropriate SMU or upgrade to a fixed Cisco IOS XR Software release. See the Fixed Software section of this advisory for additional information.
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There are no workarounds that address this vulnerability.
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Cisco considers any workarounds and mitigations (if applicable) to be temporary solutions until an upgrade to a fixed software release is available. To fully remediate this vulnerability and avoid future exposure as described in this advisory, Cisco strongly recommends that customers upgrade to the fixed software indicated in this advisory.
Fixed Releases
In the following table, the left column lists Cisco software releases or trains. The right column indicates whether a release (train) is affected by the vulnerability that is described in this advisory and the first release that includes the fix for this vulnerability.
Cisco IOS XR Software Releases First Fixed Release 7.8.2 and earlier Not affected. 7.9 Migrate to a fixed release or apply SMU. 7.10 Migrate to a fixed release or apply SMU. 7.11 Migrate to a fixed release or apply SMU. 24.1 Migrate to a fixed release or apply SMU. 24.2 Migrate to a fixed release or apply SMU. 24.3 Migrate to a fixed release or apply SMU. 24.4 Migrate to a fixed release or apply SMU. 25.1 Migrate to a fixed release or apply SMU. 25.2 Not vulnerable. 25.3 Not vulnerable. 25.4 Not vulnerable. 26.1 Not vulnerable. The following SMUs have been made public to address this issue.
Cisco IOS XR Software Release Cisco Bug ID SMU Name 7.9.2 CSCws66900 ncs5500-7.9.2.CSCws66900
ncs5700-7.9.2.CSCws66900
iosxrwbd-7.9.2.CSCws669007.10.2 CSCws66892 ncs5500-7.10.2.CSCws66892
ncs5700-7.10.2.CSCws668927.11.2 CSCws66900 ncs5500-7.11.2.CSCws66900
ncs5700-7.11.2.CSCws66900
iosxrwbd-7.11.2.CSCws669007.11.21 CSCws66900 ncs5500-7.11.21.CSCws66900
ncs5700-7.11.21.CSCws6690024.1.2 CSCws66892 ncs5500-24.1.2.CSCws66892
ncs5700-24.1.2.CSCws6689224.2.2 CSCws66892 ncs5500-24.2.2.CSCws66892
ncs5700-24.2.2.CSCws6689224.2.21 CSCws66900 ncs5500-24.2.21.CSCws66900
ncs5700-24.2.21.CSCws6690024.3.2 CSCws66900 ncs5500-24.3.2.CSCws66900
ncs5700-24.3.2.CSCws6690024.4.2 CSCws66900 ncs5500-24.4.2.CSCws66900
ncs5700-24.4.2.CSCws6690025.1.2 CSCws66900 ncs5500-25.1.2.CSCws66900
ncs5700-25.1.2.CSCws66900The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory.
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The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.
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This vulnerability was found during the resolution of a Cisco Technical Assistance Center (TAC) support case.
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To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
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Show LessVersion Description Section Status Date 1.0 Initial public release. — Final 2026-MAR-11
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SOFTWARE DOWNLOADS AND TECHNICAL SUPPORT
The Cisco Support and Downloads page on Cisco.com provides information about licensing and downloads. This page can also display customer device support coverage for customers who use the My Devices tool. Please note that customers may download only software that was procured from Cisco directly or through a Cisco authorized reseller or partner and for which the license is still valid.
Customers who purchase directly from Cisco but do not hold a Cisco service contract and customers who make purchases through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should obtain upgrades by contacting the Cisco Technical Assistance Center (TAC). Customers should have the product serial number available and be prepared to provide the URL of this advisory as evidence of entitlement to a free upgrade.
When considering software upgrades, customers are advised to regularly consult the advisories for the relevant Cisco products to determine exposure and a complete upgrade solution. In all cases, customers should ensure that the devices to be upgraded contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, customers are advised to contact the Cisco Technical Assistance Center (TAC) or their contracted maintenance providers.
LEGAL DISCLAIMER DETAILS
CISCO DOES NOT MAKE ANY EXPRESS OR IMPLIED GUARANTEES OR WARRANTIES OF ANY KIND, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. WITHOUT LIMITING THE GENERALITY OF THE FOREGOING, CISCO DOES NOT GUARANTEE THE ACCURACY OR COMPLETENESS OF THIS INFORMATION. THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.
Copies or summaries of the information contained in this Security Advisory may lack important information or contain factual errors. Customers are advised to visit the Cisco Security Advisories page for the most recent version of this Security Advisory. The Cisco Product Security Incident Response Team (PSIRT) assesses only the affected and fixed release information that is documented in this advisory. See the Cisco Security Vulnerability Policy for more information.