What is the CVSS score of CVE-2021-27289?

CVE-2021-27289 has a CVSS 3.1 base score of 9.1 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H. EPSS exploitation probability: 0.6%.

Is there a public PoC exploit available for CVE-2021-27289?

Yes, a public proof-of-concept exploit is available for CVE-2021-27289. Prioritise patching immediately. EPSS: 0.6%.

How to fix or mitigate CVE-2021-27289?

Within 24 hours: Identify all affected systems and apply vendor patches immediately. Monitor vendor channels for patch availability.

CVE-2021-27289

CRITICAL

Authentication Bypass by Capture-replay (CWE-294)

2025-04-15 cve@mitre.org

Code Injection

9.1

CVSS 3.1 · NVD

View

Vulnerability Assessment

Weakness	CWE CWE-294 OWASP Top 10:2025 A07:2025 - Authentication Failures ASVS 5.0 V6 - Authentication Replay attack prevention
Impact	CVSS score of 9.1 (CRITICAL). Attack characteristics: network attack vector, low complexity, no privileges required, no user interaction not required. Public proof-of-concept exploit code is available. EPSS exploitation probability: 0.55%.
Exploit ScenarioDerived	This vulnerability can be exploited remotely over the network. Successful exploitation could compromise the critical-severity affected system.

Act Now Prioritize within 24-48h. Why: CRITICAL severity + public POC available.

No patch listed yet 0.6% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 28, 2026

A replay attack vulnerability was discovered in a Zigbee smart home kit manufactured by Ksix (Zigbee Gateway Module = v1.0.3, Door Sensor = v1.0.7, Motion Sensor = v1.0.12), where the Zigbee. Rated critical severity (CVSS 9.1), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Earlier versions of this analysis (1)

v1 Mar 28, 2026 - 18:36 CVSS 9.1

RemediationAI

No vendor patch is available at time of analysis. Monitor vendor advisories for updates. Apply vendor patches when available. Implement network segmentation and monitoring as interim mitigations.

Affected ProductsAI

See vendor advisory for affected versions.

Affects your stack

Find out whether the stacks and servers you run are on an affected version.

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

This vulnerability is classified under CWE-294. A replay attack vulnerability was discovered in a Zigbee smart home kit manufactured by Ksix (Zigbee Gateway Module = v1.0.3, Door Sensor = v1.0.7, Motion Sensor = v1.0.12), where the Zigbee anti-replay mechanism - based on the frame counter field - is improperly implemented. As a result, an attacker within wireless range can resend captured packets with a higher sequence number, which the devices incorrectly accept as legitimate messages. This allows spoofed commands to be injected without authentication, triggering false alerts and misleading the user through notifications in the mobile application used to monitor the network.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 9.1 CRITICAL

AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

High

Availability

High

Lifecycle Timeline

PoC Detected

Apr 16, 2025 - 15:15 vuln.today

Public exploit code

CVE Published

Apr 15, 2025 - 18:15 nvd

CRITICAL 9.1

DescriptionCVE.org

A replay attack vulnerability was discovered in a Zigbee smart home kit manufactured by Ksix (Zigbee Gateway Module = v1.0.3, Door Sensor = v1.0.7, Motion Sensor = v1.0.12), where the Zigbee anti-replay mechanism - based on the frame counter field - is improperly implemented. As a result, an attacker within wireless range can resend captured packets with a higher sequence number, which the devices incorrectly accept as legitimate messages. This allows spoofed commands to be injected without authentication, triggering false alerts and misleading the user through notifications in the mobile application used to monitor the network.

Executive ViewAI

Why It Matters

Organizations using A replay attack vulnerability face critical risk from CVE-2021-27289 rated CVSS 9.1. Successful exploitation could critically impact the confidentiality, integrity, and availability of affected systems. Proof-of-concept code is publicly available, increasing the risk of exploitation. Organizations should apply vendor updates immediately when available and implement compensating controls in the interim.

Business Impact: Severe

Compensating Controls

Apply vendor patch. If immediate patching is not feasible: (1) Implement network-level access controls to limit exposure; (2) Enable enhanced monitoring and alerting; (3) Apply principle of least privilege.

Threat Intelligence Overview

EPSS Score

0.6%

Top 32% exploitable

Exploit

POC

Public exploit code exists

Data Quality

5 sources

Confidence: Medium

NVD

CVE.org

EPSS

Exploit-DB

GitHub

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity CRITICAL

CISA KEV No

Public POC Yes

EPSS 0.6%

Patch available No

Active threat No

Deciding rule

CRITICAL severity + public POC available

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Out-of-Cycle

Exploitation· derived

Poc

System Exposure· derived

Open

Automatable· derived

Yes

Human Impact

Very High

Priority Score

Low Medium High Critical

KEV: 0

EPSS: +1

CVSS: +46

PoC: +20

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Code Injection CRITICAL

Code injection occurs when an application accepts user input and passes it directly into a language interpreter or evaluator without proper sanitization.