Vulnerability Database

383,371

Total vulnerabilities in the database

CVE-2021-1377 — cisco / ios

Resource Management Errors

A vulnerability in Address Resolution Protocol (ARP) management of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to prevent an affected device from resolving ARP entries for legitimate hosts on the connected subnets. This vulnerability exists because ARP entries are mismanaged. An attacker could exploit this vulnerability by continuously sending traffic that results in incomplete ARP entries. A successful exploit could allow the attacker to cause ARP requests on the device to be unsuccessful for legitimate hosts, resulting in a denial of service (DoS) condition.

  • Published: Mar 24, 2021
  • Updated: Sep 13, 2026
  • CVE: CVE-2021-1377
  • Severity: Medium
  • Exploit:
  • CISA KEV:

CVSS v3:

  • Severity: Medium
  • Score: 5.8
  • AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L

CVSS v2:

  • Severity: Medium
  • Score: 5
  • AV:N/AC:L/Au:N/C:N/I:N/A:P

CWEs:

Software Affected versions
cisco / ios = 12.2(6)i1
cisco / ios = 15.1(3)svr1
cisco / ios = 15.1(3)svr2
cisco / ios = 15.1(3)svr3
cisco / ios = 15.1(3)svs
cisco / ios = 15.1(3)svs1
cisco / ios = 15.2(2)e6
cisco / ios = 15.2(2)e7
cisco / ios = 15.2(2)e7b
cisco / ios = 15.2(2)e8
cisco / ios = 15.2(2)e9
cisco / ios = 15.2(2)e9a
cisco / ios = 15.2(2)e10
cisco / ios = 15.2(3)e5
cisco / ios = 15.2(4)e4
cisco / ios = 15.2(4)e5
cisco / ios = 15.2(4)e5a
cisco / ios = 15.2(4)e6
cisco / ios = 15.2(4)e7
cisco / ios = 15.2(4)e8
cisco / ios = 15.2(4)e9
cisco / ios = 15.2(4)e10
cisco / ios = 15.2(4)e10a
cisco / ios = 15.2(4)ea6
cisco / ios = 15.2(4)ea7
cisco / ios = 15.2(4)ea8
cisco / ios = 15.2(4)ea9
cisco / ios = 15.2(4)ea9a
cisco / ios = 15.2(4)ea10
cisco / ios = 15.2(5)e1
cisco / ios = 15.2(5)e2
cisco / ios = 15.2(5)e2b
cisco / ios = 15.2(5)e2c
cisco / ios = 15.2(5)ex
cisco / ios = 15.2(5a)e1
cisco / ios = 15.2(6)e
cisco / ios = 15.2(6)e0a
cisco / ios = 15.2(6)e0c
cisco / ios = 15.2(6)e1
cisco / ios = 15.2(6)e1a
cisco / ios = 15.2(6)e1s
cisco / ios = 15.2(6)e2
cisco / ios = 15.2(6)e2a
cisco / ios = 15.2(6)e2b
cisco / ios = 15.2(6)e3
cisco / ios = 15.2(6)eb
cisco / ios = 15.2(7)e
cisco / ios = 15.2(7)e0a
cisco / ios = 15.2(7)e0b
cisco / ios = 15.2(7)e0s
cisco / ios = 15.2(7)e1
cisco / ios = 15.2(7)e1a
cisco / ios = 15.2(7)e2
cisco / ios = 15.2(7)e2a
cisco / ios = 15.2(7)e2b
cisco / ios = 15.2(7)e3
cisco / ios = 15.2(7a)e0b
cisco / ios = 15.2(7b)e0b
cisco / ios = 15.3(3)jpc97
cisco / ios = 15.4(1)sy
cisco / ios = 15.4(1)sy1
cisco / ios = 15.4(1)sy2
cisco / ios = 15.4(1)sy3
cisco / ios = 15.4(1)sy4
cisco / ios = 15.5(1)sy
cisco / ios = 15.5(1)sy1
cisco / ios = 15.5(1)sy2
cisco / ios = 15.5(1)sy3
cisco / ios = 15.5(1)sy4
cisco / ios = 15.5(1)sy5
cisco / ios = 15.5(1)sy6
cisco / ios = 15.5(3)m4
cisco / ios = 15.5(3)m4a
cisco / ios = 15.5(3)m4b
cisco / ios = 15.5(3)m4c
cisco / ios = 15.5(3)m5
cisco / ios = 15.5(3)m6
cisco / ios = 15.5(3)m6a
cisco / ios = 15.5(3)m7
cisco / ios = 15.5(3)m8
cisco / ios = 15.5(3)m9
cisco / ios = 15.5(3)m10
cisco / ios = 15.5(3)m11
cisco / ios = 15.5(3)s4
cisco / ios = 15.5(3)s5
cisco / ios = 15.5(3)s6
cisco / ios = 15.5(3)s6a
cisco / ios = 15.5(3)s6b
cisco / ios = 15.5(3)s7
cisco / ios = 15.5(3)s8
cisco / ios = 15.5(3)s9
cisco / ios = 15.5(3)s9a
cisco / ios = 15.5(3)s10
cisco / ios = 15.5(3)s10a
cisco / ios = 15.6(3)m2
cisco / ios = 15.6(3)m2a
cisco / ios = 15.6(3)m3
cisco / ios = 15.6(3)m3a
cisco / ios = 15.6(3)m4
cisco / ios = 15.6(3)m5
cisco / ios = 15.6(3)m6
cisco / ios = 15.6(3)m6a
cisco / ios = 15.6(3)m6b
cisco / ios = 15.6(3)m7
cisco / ios = 15.6(3)m8
cisco / ios = 15.6(3)m9
cisco / ios = 15.7(3)m
cisco / ios = 15.7(3)m0a
cisco / ios = 15.7(3)m1
cisco / ios = 15.7(3)m2
cisco / ios = 15.7(3)m3
cisco / ios = 15.7(3)m4
cisco / ios = 15.7(3)m4a
cisco / ios = 15.7(3)m4b
cisco / ios = 15.7(3)m5
cisco / ios = 15.7(3)m6
cisco / ios = 15.7(3)m7
cisco / ios = 15.8(3)m
cisco / ios = 15.8(3)m0a
cisco / ios = 15.8(3)m0b
cisco / ios = 15.8(3)m1
cisco / ios = 15.8(3)m1a
cisco / ios = 15.8(3)m2
cisco / ios = 15.8(3)m2a
cisco / ios = 15.8(3)m3
cisco / ios = 15.8(3)m3a
cisco / ios = 15.8(3)m3b
cisco / ios = 15.8(3)m4
cisco / ios = 15.8(3)m5
cisco / ios = 15.9(3)m
cisco / ios = 15.9(3)m0a
cisco / ios = 15.9(3)m1
cisco / ios = 15.9(3)m2
cisco / ios = 15.9(3)m2a
cisco / ios_xe = 3.6.6e
cisco / ios_xe = 3.6.7ae
cisco / ios_xe = 3.6.7be
cisco / ios_xe = 3.6.7e
cisco / ios_xe = 3.6.8e
cisco / ios_xe = 3.6.9ae
cisco / ios_xe = 3.6.9e
cisco / ios_xe = 3.6.10e
cisco / ios_xe = 3.7.5e
cisco / ios_xe = 3.8.4e
cisco / ios_xe = 3.8.5ae
cisco / ios_xe = 3.8.5e
cisco / ios_xe = 3.8.6e
cisco / ios_xe = 3.8.7e
cisco / ios_xe = 3.8.8e
cisco / ios_xe = 3.8.9e
cisco / ios_xe = 3.8.10e
cisco / ios_xe = 3.9.1e
cisco / ios_xe = 3.9.2be
cisco / ios_xe = 3.9.2e
cisco / ios_xe = 3.10.0ce
cisco / ios_xe = 3.10.0e
cisco / ios_xe = 3.10.1ae
cisco / ios_xe = 3.10.1e
cisco / ios_xe = 3.10.1se
cisco / ios_xe = 3.10.2e
cisco / ios_xe = 3.10.3e
cisco / ios_xe = 3.11.0e
cisco / ios_xe = 3.11.1ae
cisco / ios_xe = 3.11.1e
cisco / ios_xe = 3.11.2ae
cisco / ios_xe = 3.11.2e
cisco / ios_xe = 3.11.3ae
cisco / ios_xe = 3.11.3e
cisco / ios_xe = 3.16.4as
cisco / ios_xe = 3.16.4bs
cisco / ios_xe = 3.16.4cs
cisco / ios_xe = 3.16.4ds
cisco / ios_xe = 3.16.4es
cisco / ios_xe = 3.16.4gs
cisco / ios_xe = 3.16.4s
cisco / ios_xe = 3.16.5as
cisco / ios_xe = 3.16.5bs
cisco / ios_xe = 3.16.5s
cisco / ios_xe = 3.16.6bs
cisco / ios_xe = 3.16.6s
cisco / ios_xe = 3.16.7as
cisco / ios_xe = 3.16.7bs
cisco / ios_xe = 3.16.7s
cisco / ios_xe = 3.16.8s
cisco / ios_xe = 3.16.9s
cisco / ios_xe = 3.16.10as
cisco / ios_xe = 3.16.10s
cisco / ios_xe = 16.3.2
cisco / ios_xe = 16.3.3
cisco / ios_xe = 16.3.4
cisco / ios_xe = 16.3.5
cisco / ios_xe = 16.3.5b
cisco / ios_xe = 16.3.6
cisco / ios_xe = 16.3.7
cisco / ios_xe = 16.3.8
cisco / ios_xe = 16.3.9
cisco / ios_xe = 16.3.10
cisco / ios_xe = 16.3.11
cisco / ios_xe = 16.4.1
cisco / ios_xe = 16.4.2
cisco / ios_xe = 16.4.3
cisco / ios_xe = 16.5.1
cisco / ios_xe = 16.5.1a
cisco / ios_xe = 16.5.1b
cisco / ios_xe = 16.5.2
cisco / ios_xe = 16.5.3
cisco / ios_xe = 16.6.1
cisco / ios_xe = 16.6.2
cisco / ios_xe = 16.6.3
cisco / ios_xe = 16.6.4
cisco / ios_xe = 16.6.4a
cisco / ios_xe = 16.6.4s
cisco / ios_xe = 16.6.5
cisco / ios_xe = 16.6.5a
cisco / ios_xe = 16.6.5b
cisco / ios_xe = 16.6.6
cisco / ios_xe = 16.6.7
cisco / ios_xe = 16.6.7a
cisco / ios_xe = 16.6.8
cisco / ios_xe = 16.7.1
cisco / ios_xe = 16.7.1a
cisco / ios_xe = 16.7.1b
cisco / ios_xe = 16.7.2
cisco / ios_xe = 16.7.3
cisco / ios_xe = 16.7.4
cisco / ios_xe = 16.8.1
cisco / ios_xe = 16.8.1a
cisco / ios_xe = 16.8.1b
cisco / ios_xe = 16.8.1c
cisco / ios_xe = 16.8.1d
cisco / ios_xe = 16.8.1e
cisco / ios_xe = 16.8.1s
cisco / ios_xe = 16.8.2
cisco / ios_xe = 16.8.3
cisco / ios_xe = 16.9.1
cisco / ios_xe = 16.9.1a
cisco / ios_xe = 16.9.1b
cisco / ios_xe = 16.9.1c
cisco / ios_xe = 16.9.1d
cisco / ios_xe = 16.9.1s
cisco / ios_xe = 16.9.2
cisco / ios_xe = 16.9.2a
cisco / ios_xe = 16.9.2s
cisco / ios_xe = 16.9.3
cisco / ios_xe = 16.9.3a
cisco / ios_xe = 16.9.3h
cisco / ios_xe = 16.9.3s
cisco / ios_xe = 16.9.4
cisco / ios_xe = 16.9.4c
cisco / ios_xe = 16.9.5
cisco / ios_xe = 16.9.5f
cisco / ios_xe = 16.9.6
cisco / ios_xe = 16.10.1
cisco / ios_xe = 16.10.1a
cisco / ios_xe = 16.10.1b
cisco / ios_xe = 16.10.1c
cisco / ios_xe = 16.10.1d
cisco / ios_xe = 16.10.1e
cisco / ios_xe = 16.10.1f
cisco / ios_xe = 16.10.1g
cisco / ios_xe = 16.10.1s
cisco / ios_xe = 16.10.2
cisco / ios_xe = 16.10.3
cisco / ios_xe = 16.11.1
cisco / ios_xe = 16.11.1a
cisco / ios_xe = 16.11.1b
cisco / ios_xe = 16.11.1c
cisco / ios_xe = 16.11.1s
cisco / ios_xe = 16.11.2
cisco / ios_xe = 16.12.1
cisco / ios_xe = 16.12.1a
cisco / ios_xe = 16.12.1c
cisco / ios_xe = 16.12.1s
cisco / ios_xe = 16.12.1t
cisco / ios_xe = 16.12.1w
cisco / ios_xe = 16.12.1x
cisco / ios_xe = 16.12.1y
cisco / ios_xe = 16.12.1z
cisco / ios_xe = 16.12.2
cisco / ios_xe = 16.12.2a
cisco / ios_xe = 16.12.2s
cisco / ios_xe = 16.12.2t
cisco / ios_xe = 16.12.3
cisco / ios_xe = 16.12.3a
cisco / ios_xe = 16.12.3s
cisco / ios_xe = 16.12.4
cisco / ios_xe = 16.12.4a
cisco / ios_xe = 17.1.1
cisco / ios_xe = 17.1.1a
cisco / ios_xe = 17.1.1s
cisco / ios_xe = 17.1.1t
cisco / ios_xe = 17.1.2
cisco / ios_xe = 17.2.1
cisco / ios_xe = 17.2.1a
cisco / ios_xe = 17.2.1r
cisco / ios_xe = 17.2.1v
cisco / ios_xe = 17.2.2
cisco / ios_xe = 17.3.1
cisco / ios_xe = 17.3.1a
cisco / ios_xe = 17.3.1w
cisco / ios_xe = 17.3.2
cisco / ios_xe = 17.3.2a

Frequently Asked Questions

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.