Cisco Security Advisory
Cisco IOS XE Software for Catalyst 9000 Series Switches Denial of Service Vulnerability
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CVSS:3.1/AV:A/AC:L/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 certain Ethernet frames in Cisco IOS XE Software for Catalyst 9000 Series Switches could allow an unauthenticated, adjacent attacker to cause an egress port to become blocked and drop all outbound traffic.
This vulnerability is due to improper handling of crafted Ethernet frames. An attacker could exploit this vulnerability by sending crafted Ethernet frames through an affected switch. A successful exploit could allow the attacker to cause the egress port to which the crafted frame is forwarded to start dropping all frames, resulting in a denial of service (DoS) condition.
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-cat9k-PtmD7bgyThis advisory is part of the September 2025 release of the Cisco IOS and IOS XE Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: September 2025 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication.
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Vulnerable Products
This vulnerability affects the following Cisco Catalyst 9000 switching family platforms if they are running a vulnerable release of Cisco IOS XE Software and have a trunk port, or a Cisco TrustSec-enabled port, or a MACSec-enabled port enabled:
- Catalyst 9200 Series Switches
- Catalyst 9300 Series Switches
- Catalyst 9400 Series Switches
- Catalyst 9500 Series Switches
- Catalyst 9600 Series Switches
Meraki MS390 and Cisco Catalyst 9300 Series Switches that are running software earlier than Meraki CS 17.2.2 are affected. Cloud-Managed Hybrid Operating Mode for Catalyst Wireless LAN Controllers that are running Cisco IOS XE Software releases earlier than Release 17.15.4 are also affected. This is fixed in Cisco IOS XE Software Release 17.15.4.
For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.
Determine the Device Configuration
Determine Whether a Trunk Port is Enabled on a Device
To determine whether a device has a trunk port enabled, use Administrator privileges to connect to the device CLI and use the show running-config | include switchport mode trunk|dynamic|dot1q-tunnel command. If output is returned, the device is affected, as shown in the following example:
Switch#show running-config | include switchport mode trunk|dynamic|dot1q-tunnel
switchport mode trunk
Switch#Determine Whether a Device Has a Cisco TrustSec-Enabled Port
To determine whether a device has a Cisco TrustSec-enabled port, use Administrator privileges to connect the device CLI and use the show running-config | include cts manual command. If output is returned, the device is affected, as shown in the following example:
Switch#show running-config | include cts manual
cts manual
Switch#Determine Whether a Device Has a MACsec-Enabled Port
To determine whether a device has a MACsec-enabled port, use Administrator privileges to connect to the device CLI and use the show macsec summary command. If the returned output includes any interfaces, the device is affected, as shown in the following example:
Switch#show macsec summary
Interface Transmit SC Receive SC
Gi1/0/1 0 0
Switch#Products 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:
- Catalyst 9800 Series Wireless Controllers
- IE9300 Rugged Series Switches
- IOS Software
- IOS XR Software
- NX-OS Software
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The handling of certain crafted Ethernet frames could result in the egress port FIFO queue of the affected port becoming stuck, which would result in the port dropping all outbound traffic, as shown in the following example:
Switch#show interfaces tenGigabitEthernet 6/0/1 | include Total output drops
Input queue: 0/375/0/0 (size/max/drops/flushes); Total output drops: 461992
Switch#Repeating the command multiple times will show a continuous increase in the Total output drops, which is an indication that traffic is not being forwarded through the interface.
To recover from this condition, first, identify the source of the crafted frames. Then, either remove that device or block that device by using either VLAN or MAC ACLs. Once the source of the crafted frames has been removed, reload the device. This is the only way to recover the device.
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There are no workarounds that address this vulnerability.
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Cisco considers any workarounds and mitigations 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.
Cisco IOS and IOS XE Software
To help customers determine their exposure to vulnerabilities in Cisco IOS and IOS XE Software, Cisco provides the Cisco Software Checker. This tool identifies any Cisco security advisories that impact a specific software release and the earliest release that fixes the vulnerabilities that are described in each advisory (“First Fixed”). If applicable, the tool also returns the earliest release that fixes all the vulnerabilities that are described in all the advisories that the Software Checker identifies (“Combined First Fixed”).
To use the tool, go to the Cisco Software Checker page and follow the instructions. Alternatively, use the following form to determine whether a release is affected by any Cisco Security Advisory. To use the form, follow these steps:
- Choose which advisories the tool will search-only this advisory, only advisories with a Critical or High Security Impact Rating (SIR), or all advisories.
- Enter a release number-for example, 15.9(3)M2 or 17.3.3.
- Click Check.
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The Cisco Product Security Incident Response Team (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 1.1 Updated the first sentence to clarify the feature information. Vulnerable Products Final 2025-SEP-30 1.0 Initial public release. - Final 2025-SEP-30
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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.