CVE-2021-1368

Cisco FXOS and NX-OS Software Unidirectional Link Detection Denial of Service and Arbitrary Code Execution Vulnerability

HIGH

8.8

CVSS Score

Published: February 24, 2021 at 07:30 PM UTC

Updated: June 17, 2026 at 03:31 AM UTC

101 products affected across 1 vendorNx OSUnified Computing SystemFirepower Extensible Operating System

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Severity

HIGH8.8

Exploit prediction

EPSS 0.5%

SSVC

No known exploit

Description

A vulnerability in the Unidirectional Link Detection (UDLD) feature of Cisco FXOS Software and Cisco NX-OS Software could allow an unauthenticated, adjacent attacker to execute arbitrary code with administrative privileges or cause a denial of service (DoS) condition on an affected device. This vulnerability is due to insufficient input validation. An attacker could exploit this vulnerability by sending crafted Cisco UDLD protocol packets to a directly connected, affected device. A successful exploit could allow the attacker to execute arbitrary code with administrative privileges or cause the Cisco UDLD process to crash and restart multiple times, causing the affected device to reload and resulting in a DoS condition. Note: The UDLD feature is disabled by default, and the conditions to exploit this vulnerability are strict. The attacker needs full control of a directly connected device. That device must be connected over a port channel that has UDLD enabled. To trigger arbitrary code execution, both the UDLD-enabled port channel and specific system conditions must exist. In the absence of either the UDLD-enabled port channel or the system conditions, attempts to exploit this vulnerability will result in a DoS condition. It is possible, but highly unlikely, that an attacker could control the necessary conditions for exploitation. The CVSS score reflects this possibility. However, given the complexity of exploitation, Cisco has assigned a Medium Security Impact Rating (SIR) to this vulnerability.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Firepower Extensible Operating System · Cisco

95%

r231

cisco-firepower-4110 (environment) · cisco-firepower-4112 (environment) · cisco-firepower-4115 (environment) · cisco-firepower-4120 (environment) · cisco-firepower-4125 (environment) · cisco-firepower-4140 (environment) · cisco-firepower-4145 (environment) · cisco-firepower-4150 (environment) · cisco-firepower-9300 (environment)

Nx OS · Cisconpm

95%

7.0(3)i5(2)7.0(3)i7(9)7.3(8)n1(1)7.3(9)n1(0.823)8.4(3.108)8.4(3.117)9.3(5)

cisco-mds-9148s (environment) · cisco-mds-9250i (environment) · cisco-mds-9706 (environment) · cisco-mds-9710 (environment) · cisco-nexus-3048 (environment) · cisco-nexus-31108pv-v (environment) · cisco-nexus-31108tc-v (environment) · cisco-nexus-31128pq (environment) · cisco-nexus-3132c-z (environment) · cisco-nexus-3132q-v (environment) · cisco-nexus-3132q-x (environment) · cisco-nexus-3132q-xl (environment) · cisco-nexus-3164q (environment) · cisco-nexus-3172pq (environment) · cisco-nexus-3172pq-xl (environment) · cisco-nexus-3232c (environment) · cisco-nexus-3264c-e (environment) · cisco-nexus-3264q (environment) · cisco-nexus-3408-s (environment) · cisco-nexus-34180yc (environment) · cisco-nexus-3432d-s (environment) · cisco-nexus-3464c (environment) · cisco-nexus-3524-x (environment) · cisco-nexus-3524-xl (environment) · cisco-nexus-3548-x (environment) · cisco-nexus-3548-xl (environment) · cisco-nexus-36180yc-r (environment) · cisco-nexus-3636c-r (environment) · cisco-nexus-5548p (environment) · cisco-nexus-5548up (environment) · cisco-nexus-5596t (environment) · cisco-nexus-5596up (environment) · cisco-nexus-56128p (environment) · cisco-nexus-5624q (environment) · cisco-nexus-5648q (environment) · cisco-nexus-5672up (environment) · cisco-nexus-5672up-16g (environment) · cisco-nexus-5696q (environment) · cisco-nexus-6001 (environment) · cisco-nexus-6004 (environment) · cisco-nexus-7000 (environment) · cisco-nexus-7700 (environment) · cisco-nexus-9000v (environment) · cisco-nexus-92160yc-x (environment) · cisco-nexus-9221c (environment) · cisco-nexus-92300yc (environment) · cisco-nexus-92304qc (environment) · cisco-nexus-92348gc-x (environment) · cisco-nexus-9236c (environment) · cisco-nexus-9272q (environment) · cisco-nexus-93108tc-ex (environment) · cisco-nexus-93108tc-ex-24 (environment) · cisco-nexus-93108tc-fx (environment) · cisco-nexus-93108tc-fx-24 (environment) · cisco-nexus-93120tx (environment) · cisco-nexus-93128tx (environment) · cisco-nexus-9316d-gx (environment) · cisco-nexus-93180lc-ex (environment) · cisco-nexus-93180yc-ex (environment) · cisco-nexus-93180yc-ex-24 (environment) · cisco-nexus-93180yc-fx (environment) · cisco-nexus-93180yc-fx-24 (environment) · cisco-nexus-93180yc-fx3 (environment) · cisco-nexus-93180yc-fx3s (environment) · cisco-nexus-93216tc-fx2 (environment) · cisco-nexus-93240yc-fx2 (environment) · cisco-nexus-9332pq (environment) · cisco-nexus-93360yc-fx2 (environment) · cisco-nexus-9336c-fx2 (environment) · cisco-nexus-9336c-fx2-e (environment) · cisco-nexus-9336pq (environment) · cisco-nexus-9348gc-fxp (environment) · cisco-nexus-93600cd-gx (environment) · cisco-nexus-9364c (environment) · cisco-nexus-9364c-gx (environment) · cisco-nexus-9372px (environment) · cisco-nexus-9372px-e (environment) · cisco-nexus-9372tx (environment) · cisco-nexus-9372tx-e (environment) · cisco-nexus-9396px (environment) · cisco-nexus-9396tx (environment) · cisco-nexus-9508 (environment)

Unified Computing System · Cisco

95%

v < 4.0(4i)4.1 ≤ v < 4.1(2c)

Affected range stops below 4.0(4i), so it looks safe — our inference, not a vendor statement

Affected range stops below 4.1(2c), so it looks safe — our inference, not a vendor statement

cisco-ucs-6248up (environment) · cisco-ucs-6296up (environment) · cisco-ucs-6324 (environment) · cisco-ucs-6332 (environment) · cisco-ucs-6332-16up (environment) · cisco-ucs-64108 (environment) · cisco-ucs-6454 (environment)

Firepower 4110 · Ciscodevice

80%

All versions

Firepower 4112 · Ciscodevice

80%

All versions

Firepower 4115 · Ciscodevice

80%

All versions

Firepower 4120 · Ciscodevice

80%

All versions