Vulnerability Database

393,392

Total vulnerabilities in the database

CVE-2026-20301 — cisco / ios

Unchecked Input for Loop Condition

A vulnerability in the Extensible Messaging Client Protocol (XMCP), also referred to as the External Client protocol, of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device.

This vulnerability is due to improper handling of malformed XMCP packets. An attacker could exploit this vulnerability by sending a malformed XMCP packet to an affected device. A successful exploit could allow the attacker to cause the affected device to reload unexpectedly, resulting in a DoS condition. The attacker does not need the XMCP client username to exploit this vulnerability.

  • Published: Aug 5, 2026
  • Updated: Oct 3, 2026
  • CVE: CVE-2026-20301
  • Severity: High
  • Exploit:
  • CISA KEV:

CVSS v3:

  • Severity: High
  • Score: 8.6
  • AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

CWEs:

Software Affected versions
cisco / ios = 15.2(1)sy6
cisco / ios = 15.2(1)sy7
cisco / ios = 15.2(1)sy8
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(2)e10a
cisco / ios = 15.2(2)e10b
cisco / ios = 15.2(2)e10c
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)e10b
cisco / ios = 15.2(4)e10c
cisco / ios = 15.2(4)e10d
cisco / ios = 15.2(4)e10e
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(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(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)e2b
cisco / ios = 15.2(7)e3
cisco / ios = 15.2(7)e3k
cisco / ios = 15.2(7)e4
cisco / ios = 15.2(7)e5
cisco / ios = 15.2(7)e6
cisco / ios = 15.2(7)e7
cisco / ios = 15.2(7)e8
cisco / ios = 15.2(7)e9
cisco / ios = 15.2(7)e10
cisco / ios = 15.2(7)e11
cisco / ios = 15.2(7)e12
cisco / ios = 15.2(7)e13
cisco / ios = 15.2(7)e14
cisco / ios = 15.2(8)e
cisco / ios = 15.2(8)e1
cisco / ios = 15.2(8)e2
cisco / ios = 15.2(8)e3
cisco / ios = 15.2(8)e4
cisco / ios = 15.2(8)e5
cisco / ios = 15.2(8)e6
cisco / ios = 15.2(8)e7
cisco / ios = 15.2(8)e8
cisco / ios = 15.4(1)sy4
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(1)sy7
cisco / ios = 15.5(1)sy8
cisco / ios = 15.5(1)sy9
cisco / ios = 15.5(1)sy10
cisco / ios = 15.5(1)sy11
cisco / ios = 15.5(1)sy12
cisco / ios = 15.5(1)sy13
cisco / ios = 15.5(1)sy14
cisco / ios = 15.5(1)sy15
cisco / ios = 15.5(1)sy16
cisco / ios = 15.5(1)sy17
cisco / ios = 15.6(2)sp4
cisco / ios = 15.6(2)sp5
cisco / ios = 15.6(2)sp6
cisco / ios = 15.6(2)sp7
cisco / ios = 15.6(2)sp8
cisco / ios = 15.6(2)sp8a
cisco / ios = 15.6(2)sp9
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 = 15.7(3)m8
cisco / ios = 15.7(3)m9
cisco / ios = 15.7(3)m10
cisco / ios = 15.7(3)m10a
cisco / ios = 15.7(3)m10b
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 = 15.8(3)m6
cisco / ios = 15.8(3)m7
cisco / ios = 15.8(3)m8
cisco / ios = 15.8(3)m9
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 = 15.9(3)m3
cisco / ios = 15.9(3)m3a
cisco / ios = 15.9(3)m3b
cisco / ios = 15.9(3)m4
cisco / ios = 15.9(3)m4a
cisco / ios = 15.9(3)m5
cisco / ios = 15.9(3)m6
cisco / ios = 15.9(3)m6a
cisco / ios = 15.9(3)m6b
cisco / ios = 15.9(3)m7
cisco / ios = 15.9(3)m7a
cisco / ios = 15.9(3)m8
cisco / ios = 15.9(3)m8a
cisco / ios = 15.9(3)m8b
cisco / ios = 15.9(3)m9
cisco / ios = 15.9(3)m9a
cisco / ios = 15.9(3)m10
cisco / ios = 15.9(3)m11
cisco / ios = 15.9(3)m12
cisco / ios = 15.9(3)m13
cisco / ios_xe = 3.8.10ce
cisco / ios_xe = 3.8.10de
cisco / ios_xe = 3.11.3ae
cisco / ios_xe = 3.11.3e
cisco / ios_xe = 3.11.4e
cisco / ios_xe = 3.11.5e
cisco / ios_xe = 3.11.6e
cisco / ios_xe = 3.11.7e
cisco / ios_xe = 3.11.8e
cisco / ios_xe = 3.11.9e
cisco / ios_xe = 3.11.10e
cisco / ios_xe = 3.11.11e
cisco / ios_xe = 3.11.12e
cisco / ios_xe = 3.11.13e
cisco / ios_xe = 3.11.14e
cisco / ios_xe = 3.16.10as
cisco / ios_xe = 3.16.10bs
cisco / ios_xe = 3.18.8asp
cisco / ios_xe = 3.18.9sp
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 = 16.6.9
cisco / ios_xe = 16.6.10
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 = 16.9.7
cisco / ios_xe = 16.9.8
cisco / ios_xe = 16.9.8a
cisco / ios_xe = 16.9.8b
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 = 16.12.1z1
cisco / ios_xe = 16.12.1z2
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 = 16.12.5
cisco / ios_xe = 16.12.5a
cisco / ios_xe = 16.12.5b
cisco / ios_xe = 16.12.6
cisco / ios_xe = 16.12.6a
cisco / ios_xe = 16.12.7
cisco / ios_xe = 16.12.8
cisco / ios_xe = 16.12.9
cisco / ios_xe = 16.12.10
cisco / ios_xe = 16.12.10a
cisco / ios_xe = 16.12.11
cisco / ios_xe = 16.12.12
cisco / ios_xe = 16.12.13
cisco / ios_xe = 16.12.14
cisco / ios_xe = 16.12.15
cisco / ios_xe = 16.12.16
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 = 17.1.3
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 = 17.2.3
cisco / ios_xe = 17.3.1
cisco / ios_xe = 17.3.1a
cisco / ios_xe = 17.3.1w
cisco / ios_xe = 17.3.1x
cisco / ios_xe = 17.3.1z
cisco / ios_xe = 17.3.2
cisco / ios_xe = 17.3.2a
cisco / ios_xe = 17.3.3
cisco / ios_xe = 17.3.3a
cisco / ios_xe = 17.3.4
cisco / ios_xe = 17.3.4a
cisco / ios_xe = 17.3.4b
cisco / ios_xe = 17.3.4c
cisco / ios_xe = 17.3.5
cisco / ios_xe = 17.3.5a
cisco / ios_xe = 17.3.5b
cisco / ios_xe = 17.3.6
cisco / ios_xe = 17.3.7
cisco / ios_xe = 17.3.8
cisco / ios_xe = 17.3.8a
cisco / ios_xe = 17.4.1
cisco / ios_xe = 17.4.1a
cisco / ios_xe = 17.4.1b
cisco / ios_xe = 17.4.1c
cisco / ios_xe = 17.4.2
cisco / ios_xe = 17.4.2a
cisco / ios_xe = 17.5.1
cisco / ios_xe = 17.5.1a
cisco / ios_xe = 17.6.1
cisco / ios_xe = 17.6.1a
cisco / ios_xe = 17.6.1x
cisco / ios_xe = 17.6.1z
cisco / ios_xe = 17.6.1z1
cisco / ios_xe = 17.6.2
cisco / ios_xe = 17.6.3
cisco / ios_xe = 17.6.3a
cisco / ios_xe = 17.6.4
cisco / ios_xe = 17.6.5
cisco / ios_xe = 17.6.5a
cisco / ios_xe = 17.6.6
cisco / ios_xe = 17.6.6a
cisco / ios_xe = 17.6.7
cisco / ios_xe = 17.6.8
cisco / ios_xe = 17.6.8a
cisco / ios_xe = 17.7.1
cisco / ios_xe = 17.7.1a
cisco / ios_xe = 17.7.1b
cisco / ios_xe = 17.7.2
cisco / ios_xe = 17.8.1
cisco / ios_xe = 17.8.1a
cisco / ios_xe = 17.9.1
cisco / ios_xe = 17.9.1a
cisco / ios_xe = 17.9.1w
cisco / ios_xe = 17.9.1x
cisco / ios_xe = 17.9.1x1
cisco / ios_xe = 17.9.1y
cisco / ios_xe = 17.9.1y1
cisco / ios_xe = 17.9.2
cisco / ios_xe = 17.9.2a
cisco / ios_xe = 17.9.3
cisco / ios_xe = 17.9.3a
cisco / ios_xe = 17.9.4
cisco / ios_xe = 17.9.4a
cisco / ios_xe = 17.9.5
cisco / ios_xe = 17.9.5a
cisco / ios_xe = 17.9.5b
cisco / ios_xe = 17.9.5c
cisco / ios_xe = 17.9.5d
cisco / ios_xe = 17.9.5e
cisco / ios_xe = 17.9.5f
cisco / ios_xe = 17.9.6
cisco / ios_xe = 17.9.6a
cisco / ios_xe = 17.9.7
cisco / ios_xe = 17.9.7a
cisco / ios_xe = 17.9.7b
cisco / ios_xe = 17.9.8
cisco / ios_xe = 17.9.9
cisco / ios_xe = 17.10.1
cisco / ios_xe = 17.10.1a
cisco / ios_xe = 17.10.1b
cisco / ios_xe = 17.11.1
cisco / ios_xe = 17.11.1a
cisco / ios_xe = 17.12.1
cisco / ios_xe = 17.12.1a
cisco / ios_xe = 17.12.1w
cisco / ios_xe = 17.12.1x
cisco / ios_xe = 17.12.1y
cisco / ios_xe = 17.12.1z
cisco / ios_xe = 17.12.1z1
cisco / ios_xe = 17.12.1z2
cisco / ios_xe = 17.12.1z3
cisco / ios_xe = 17.12.1z4
cisco / ios_xe = 17.12.1z5
cisco / ios_xe = 17.12.1z6
cisco / ios_xe = 17.12.2
cisco / ios_xe = 17.12.2a
cisco / ios_xe = 17.12.3
cisco / ios_xe = 17.12.3a
cisco / ios_xe = 17.12.4
cisco / ios_xe = 17.12.4a
cisco / ios_xe = 17.12.4b
cisco / ios_xe = 17.12.5
cisco / ios_xe = 17.12.5a
cisco / ios_xe = 17.12.5b
cisco / ios_xe = 17.12.5c
cisco / ios_xe = 17.12.5d
cisco / ios_xe = 17.12.6
cisco / ios_xe = 17.12.6a
cisco / ios_xe = 17.12.6b
cisco / ios_xe = 17.12.7
cisco / ios_xe = 17.12.7a
cisco / ios_xe = 17.12.7b
cisco / ios_xe = 17.13.1
cisco / ios_xe = 17.13.1a
cisco / ios_xe = 17.14.1
cisco / ios_xe = 17.14.1a
cisco / ios_xe = 17.15.1
cisco / ios_xe = 17.15.1a
cisco / ios_xe = 17.15.1b
cisco / ios_xe = 17.15.1w
cisco / ios_xe = 17.15.1x
cisco / ios_xe = 17.15.1y
cisco / ios_xe = 17.15.2
cisco / ios_xe = 17.15.2a
cisco / ios_xe = 17.15.2b
cisco / ios_xe = 17.15.2c
cisco / ios_xe = 17.15.3
cisco / ios_xe = 17.15.3a
cisco / ios_xe = 17.15.3b
cisco / ios_xe = 17.15.4
cisco / ios_xe = 17.15.4a
cisco / ios_xe = 17.15.4b
cisco / ios_xe = 17.15.4c
cisco / ios_xe = 17.15.4d
cisco / ios_xe = 17.15.4s1
cisco / ios_xe = 17.15.5
cisco / ios_xe = 17.15.5a
cisco / ios_xe = 17.16.1
cisco / ios_xe = 17.16.1a
cisco / ios_xe = 17.17.1
cisco / ios_xe = 17.18.1
cisco / ios_xe = 17.18.1a
cisco / ios_xe = 17.18.1w
cisco / ios_xe = 17.18.1x
cisco / ios_xe = 17.18.1y
cisco / ios_xe = 17.18.1z
cisco / ios_xe = 17.18.2
cisco / ios_xe = 17.18.3
cisco / ios_xe = 17.18.3a
cisco / ios_xe = 26.1.1
cisco / ios_xe = 26.1.1a
cisco / ios_xe = 26.2.1ea

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.