Vulnerability Database

328,409

Total vulnerabilities in the database

CVE-2021-1377

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: Nov 16, 2025
  • CVE: CVE-2021-1377
  • Severity: Medium
  • Exploit:

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

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.