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Cisco NX-OS Software system login block-for Denial of Service Vulnerability

cisco-sa-nxos-login-blockfor-RwjGVEcu · Medium · Published · Updated

A vulnerability in the implementation of the system login block-for command for Cisco NX-OS Software could allow an unauthenticated, remote attacker to cause a login process to unexpectedly restart, causing a denial of service (DoS) condition. This vulnerability is due to a logic error in the implementation of the system login block-for command when an attack is detected and acted upon. An attacker could exploit this vulnerability by performing a brute-force login attack on an affected device. A successful exploit could allow the attacker to cause a login process to reload, which could result in a delay during authentication to the affected device. Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability. This advisory is available at the following link:https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nxos-login-blockfor-RwjGVEcu This advisory is part of the August 2021 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: August 2021 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication.

Cisco advisory ·CSAF JSON

Workarounds

There are no workarounds that address this vulnerability.

The device is only vulnerable if the system login block-for command is configured and a potential DoS attack was detected. If the command is removed using no [system] login block-for seconds attempts tries within seconds, the device is no longer vulnerable.

However, removing the system login block-for configuration weakens the security posture of the device. For additional information, see Configuring Login Parameters https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus9000/sw/93x/security/configuration/guide/b-cisco-nexus-9000-nx-os-security-configuration-guide-93x/b-cisco-nexus-9000-nx-os-security-configuration-guide-93x_chapter_011.html#task_794D196F3DD7430E93F14D9EEC7DE44B in the Configuring AAA chapter of Cisco Nexus 9000 Series NX-OS Security Configuration Guide, Release 9.3(x) https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus9000/sw/93x/security/configuration/guide/b-cisco-nexus-9000-nx-os-security-configuration-guide-93x/b-cisco-nexus-9000-nx-os-security-configuration-guide-93x_chapter_011.html .

While this mitigation has been deployed and was proven successful in a test environment, customers should determine the applicability and effectiveness in their own environment and under their own use conditions. Customers should be aware that any workaround or mitigation that is implemented may negatively impact the functionality or performance of their network based on intrinsic customer deployment scenarios and limitations. Customers should not deploy any workarounds or mitigations before first evaluating the applicability to their own environment and any impact to such environment.

CVEsCVE-2021-1590
Cisco Bug IDsCSCuz49095, CSCvw45963, CSCvx74585
CVSS ScoreBase 5.3
Base 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L/E:X/RL:X/RC:X
Product Names From Source
Cisco Unified Computing System (Managed), Cisco NX-OS Software 7.3(0)D1(1), Cisco NX-OS Software 7.3(0)DX(1), Cisco NX-OS Software 7.3(0)DY(1), Cisco NX-OS Software 7.3(0)N1(1), Cisco NX-OS Software 7.3(0)N1(1b), Cisco NX-OS Software 7.3(0)N1(1a), Cisco NX-OS Software 7.3(1)D1(1), Cisco NX-OS Software 7.3(1)DY(1), Cisco NX-OS Software 7.3(1)N1(1), Cisco NX-OS Software 7.3(2)D1(1), Cisco NX-OS Software 7.3(2)D1(2), Cisco NX-OS Software 7.3(2)D1(3), Cisco NX-OS Software 7.3(2)D1(3a), Cisco NX-OS Software 7.3(2)N1(1), Cisco NX-OS Software 7.3(2)N1(1b), Cisco NX-OS Software 7.3(2)N1(1c), Cisco NX-OS Software 7.3(3)N1(1), Cisco NX-OS Software 8.1(1), Cisco NX-OS Software 8.1(2), Cisco NX-OS Software 8.1(2a), Cisco NX-OS Software 8.1(1a), Cisco NX-OS Software 8.2(1), Cisco NX-OS Software 8.2(2), Cisco NX-OS Software 7.3(4)N1(1), Cisco NX-OS Software 7.3(4)N1(1a), Cisco NX-OS Software 7.3(5)N1(1), Cisco NX-OS Software 7.3(6)N1(1), Cisco NX-OS Software 7.3(6)N1(1a), Cisco NX-OS Software 7.3(7)N1(1), Cisco NX-OS Software 7.3(7)N1(1a), Cisco NX-OS Software 7.3(7)N1(1b), Cisco NX-OS Software 7.3(8)N1(1), Cisco NX-OS Software 7.3(8)N1(1a), Cisco NX-OS Software 7.3(8)N1(1b), Cisco NX-OS Software, Cisco MDS 9000 Multilayer Directors and Fabric Switches, Cisco Nexus 7000 Series Switches, Cisco Nexus 5000 Series Switches, Cisco Nexus 6000 Series Switches

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