CVE-2026-20171
Raw vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:HCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2026-20171 is a medium-severity Always-Incorrect Control Flow Implementation (CWE-670) vulnerability in Cisco Nexus (inferred from references). Its CVSS base score is 6.8 (Medium).
Operationally, ranked at the 38th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SA-15 (Development Process, Standards, and Tools) — see the control section below for these in your framework.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-31135
Vulnerability Data
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…
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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.
- CWE(s)
Related Threats
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V9.2.1
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation at post-design stages directly exercises control-flow paths and reveals mismatches between implemented and intended behavior.
Requiring a documented development process and supporting tools reduces the chance that incorrect control-flow logic is introduced in the first place.
Flaw identification and remediation processes can locate and correct control-flow errors once they manifest as incorrect runtime behavior.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices directly prevent incorrect control-flow implementations via reviews, testing, and static analysis.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing in development and acceptance can detect paths that deviate from intended logic.
Secure development lifecycle processes can catch incorrect control-flow logic during design and code review.
Secure coding standards and reviews directly target flawed control-flow implementations.
Change-management gates may prevent deployment of flawed logic but do not address the coding defect itself.