CVE-2021-1625

Cisco IOS XE Software Zone-Based Policy Firewall ICMP and UDP Inspection Vulnerability

MEDIUM
5.8
CVSS Score
Published: September 23, 2021 at 02:25 AM UTC
Updated: June 17, 2026 at 03:32 AM UTC
1 product affected across 1 vendorIOS Xe

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Severity
MEDIUM5.8
Exploit prediction
EPSS 0.9%
SSVC
No known exploit

Description

A vulnerability in the Zone-Based Policy Firewall feature of Cisco IOS XE Software could allow an unauthenticated, remote attacker to prevent the Zone-Based Policy Firewall from correctly classifying traffic. This vulnerability exists because ICMP and UDP responder-to-initiator flows are not inspected when the Zone-Based Policy Firewall has either Unified Threat Defense (UTD) or Application Quality of Experience (AppQoE) configured. An attacker could exploit this vulnerability by attempting to send UDP or ICMP flows through the network. A successful exploit could allow the attacker to inject traffic through the Zone-Based Policy Firewall, resulting in traffic being dropped because it is incorrectly classified or in incorrect reporting figures being produced by high-speed logging (HSL).

Affected

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

v < 17.3.2
Affected range stops below 17.3.2, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

SSVC — Action Prioritization

SSVCNo known exploitAutomatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

5.8MEDIUMcisco
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
CHANGED
Confidentiality
NONE
Integrity
LOW
Availability
NONE
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-284NVD-CWE-Other

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