Cisco NX-OS up to 16.1(4h) ACI Mode buffer access with incorrect length value

Summaryinfo

A vulnerability, which was classified as critical, has been found in Cisco NX-OS. Impacted is an unknown function of the component ACI Mode. This manipulation causes buffer access with incorrect length value. This vulnerability appears as CVE-2026-20033. The attacker needs to be present on the local network. There is no available exploit. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in Cisco NX-OS. It has been declared as critical. Affected by this vulnerability is an unknown functionality of the component ACI Mode. The manipulation with an unknown input leads to a buffer access with incorrect length value vulnerability. The CWE definition for the vulnerability is CWE-805. The product uses a sequential operation to read or write a buffer, but it uses an incorrect length value that causes it to access memory that is outside of the bounds of the buffer. As an impact it is known to affect availability. The summary by CVE is:

A vulnerability in Cisco Nexus 9000 Series Fabric Switches in ACI mode could allow an unauthenticated, adjacent attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to insufficient validation when processing specific Ethernet frames. An attacker could exploit this vulnerability by sending a crafted Ethernet frame to the management interface of an affected device. A successful exploit could allow the attacker to cause the device to reload unexpectedly, resulting in a DoS condition. Note: Only the out-of-band (OOB) management interface is affected.

It is possible to read the advisory at sec.cloudapps.cisco.com. This vulnerability is known as CVE-2026-20033 since 10/08/2025. The exploitation appears to be easy. The attack can only be done within the local network. The exploitation doesn't need any form of authentication. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 02/28/2026).

Upgrading eliminates this vulnerability.

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Productinfo

Type

• Router Operating System

Vendor

• Cisco

Name

• NX-OS

Version

• 15.2(1g)
• 15.2(2e)
• 15.2(2f)
• 15.2(2g)
• 15.2(2h)
• 15.2(3e)
• 15.2(3f)
• 15.2(3g)
• 15.2(4d)
• 15.2(4e)
• 15.2(4f)
• 15.2(5c)
• 15.2(5d)
• 15.2(5e)
• 15.2(6e)
• 15.2(6g)
• 15.2(6h)
• 15.2(7f)
• 15.2(7g)
• 15.2(8d)
• 15.2(8e)
• 15.2(8f)
• 15.2(8g)
• 15.2(8h)
• 15.2(8i)
• 15.3(1d)
• 15.3(2a)
• 15.3(2b)
• 15.3(2c)
• 15.3(2d)
• 15.3(2e)
• 15.3(2f)
• 16.0(1g)
• 16.0(1j)
• 16.0(2h)
• 16.0(2j)
• 16.0(3d)
• 16.0(3e)
• 16.0(3g)
• 16.0(4c)
• 16.0(5h)
• 16.0(5j)
• 16.0(6c)
• 16.0(6h)
• 16.0(7e)
• 16.0(8e)
• 16.0(8f)
• 16.0(8h)
• 16.0(9c)
• 16.0(9d)
• 16.0(9e)
• 16.1(1f)
• 16.1(2f)
• 16.1(2g)
• 16.1(3f)
• 16.1(3g)
• 16.1(4h)

License

• commercial

Website

• Vendor: https://www.cisco.com/

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