CVE-2021-34697

Cisco IOS XE Software Protection Against Distributed Denial of Service Attacks Feature Vulnerability

HIGH
8.6
CVSS Score
Published: September 23, 2021 at 02:25 AM UTC
Updated: June 17, 2026 at 03:56 AM UTC
1 product affected across 1 vendorIOS Xe

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Severity
HIGH8.6
Exploit prediction
EPSS 1%
SSVC
No known exploit

Description

A vulnerability in the Protection Against Distributed Denial of Service Attacks feature of Cisco IOS XE Software could allow an unauthenticated, remote attacker to conduct denial of service (DoS) attacks to or through the affected device. This vulnerability is due to incorrect programming of the half-opened connections limit, TCP SYN flood limit, or TCP SYN cookie features when the features are configured in vulnerable releases of Cisco IOS XE Software. An attacker could exploit this vulnerability by attempting to flood traffic to or through the affected device. A successful exploit could allow the attacker to initiate a DoS attack to or through an affected device.

Affected

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

17.3.1 ≤ v < 17.3.3
Affected range stops below 17.3.3, 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

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

Quick Info

StatusMODIFIED
CWE
CWE-665

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