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CVE-2026-20171

31
FAUCET Score

A vulnerability in the Border Gateway Protocol (BGP) enforce-first-as feature of Cisco Nexus 3000 Series Switches and Cisco Nexus 9000 Series Switches in standalone NX-OS mode could allow an unauthenticated, remote attacker to trigger BGP peer flaps, resulting in a denial of service (DoS) condition. This vulnerability is due to incorrect parsing of a transitive BGP attribute. An attacker could exploit this vulnerability by sending a crafted BGP update through an established BGP peer session. If the update propagates to an affected device, it could cause the device to drop the BGP session and flap with the BGP peer that is forwarding this update, resulting in a DoS condition.

First published: May 20, 2026Last modified: May 20, 2026

Impacted Technologies

VendorProductVersion(s)CPE
CiscoCisco NX-OS Software
10.2(1), 10.2(1q), 10.2(2), 10.2(2a), 10.2(3), 10.2(3t), 10.2(3v), 10.2(4), 10.2(5), 10.2(6), 10.2(7), 10.2(8), 10.2(9), 10.3(1), 10.3(2), 10.3(3), 10.3(3o), 10.3(3p), 10.3(3q), 10.3(3r), 10.3(3w), 10.3(3x), 10.3(4), 10.3(4a), 10.3(4g), 10.3(4h), 10.3(5), 10.3(6), 10.3(7), 10.3(8), 10.3(99w), 10.3(99x), 10.4(1), 10.4(2), 10.4(3), 10.4(4), 10.4(4g), 10.4(5), 10.4(6), 10.5(1), 10.5(2), 10.5(3), 10.5(3e), 10.5(3o), 10.5(3p), 10.5(3s), 10.5(3t), 10.6(1), 10.6(1s)CNA affecteddefault unknown

CVSS Data

CVSS version used by this source: 3.1

6.8MEDIUM

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
CHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
Exploitability Score
2.2
Impact Score
4.0
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.47%
Probability of exploitation in next 30 days
EPSS Percentile
37.8%
Percentile rank of EPSS score among Peer Group
As of 2026-07-24
Model: v2026.06.15
This CVE's current EPSS score of 0.0047 is in the 5th percentile among its peer group of 19,954 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.0 Bluesky, 0.0 Mastodon, and 0.2 GitHub mentions.

Media Mentions

The average CVE in this peer group has 0.0 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Remediation records are not available for this CVE.

References

sec.cloudapps.cisco.com / security/center/content/CiscoSecurityAdvisory/cisco-sa-bgp-iefab-3hb2pwtx