What is the CVSS score of CVE-2026-21718?

CVE-2026-21718 has a CVSS 3.1 base score of 10.0 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H. EPSS exploitation probability: 0.0%.

Which versions of Xweb 300d Pro Firmware are affected by CVE-2026-21718?

A critical authentication bypass vulnerability (CVE-2026-21718, CVSS 10.0) affects Copeland XWEB Pro v1.12.1 and earlier, allowing unauthenticated attackers to execute arbitrary code on affected…

How to fix or mitigate CVE-2026-21718?

Within 24 hours: Identify all systems running Copeland XWEB Pro v1.12.1 or earlier and isolate them from production networks if possible. Immediately implement network-based access controls to restrict connectivity to these systems. Within 7 days: Deploy compensating controls including WAF rules to block malicious payloads and enable enhanced logging/monitoring for suspicious authentication attempts. Contact Copeland for patch availability and timeline. Within 30 days: Either apply vendor patch immediately upon release, upgrade to a patched version, or decommission affected systems if no patch becomes available.

Xweb 300d Pro Firmware CVE-2026-21718

CRITICAL

Use of a Broken or Risky Cryptographic Algorithm (CWE-327)

2026-02-27 ics-cert@hq.dhs.gov

Authentication Bypass Xweb 300d Pro Firmware Xweb 500b Pro Firmware Xweb 500d Pro Firmware

10.0

CVSS 3.1 · NVD

Severity by source

NVD PRIMARY

10.0 CRITICAL

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

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Changed

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

Analysis Generated

Mar 12, 2026 - 21:55 vuln.today

CVE Published

Feb 27, 2026 - 01:16 nvd

CRITICAL 10.0

DescriptionCVE.org

An authentication bypass vulnerability exists in Copeland XWEB Pro version 1.12.1 and prior, enabling any attackers to bypass the authentication requirement and achieve pre-authenticated code execution on the system.

AnalysisAI

Authentication bypass in Copeland XWEB Pro HVAC controller version 1.12.1 and prior due to weak cryptographic algorithm. CVSS 10.0 — any unauthenticated attacker can gain full system access to building automation controllers.

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access

Send unauthenticated network request

Exploit

Bypass authentication mechanism

Execution

Execute arbitrary code pre-authentication

Impact

Achieve system compromise

Access

Send unauthenticated network request

Exploit

Bypass authentication mechanism

Execution

Execute arbitrary code pre-authentication

Impact

Achieve system compromise

Vulnerability AssessmentAI

Exploitation	No special conditions — remote unauthenticated exploitation against Copeland XWEB Pro version 1.12.1 and prior with default configurations. Additional conditions and limiting factors are described in the full assessment.
Risk Assessment	CVSS 10.0. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario	Attacker discovers internet-exposed XWEB Pro controller, bypasses authentication using cryptographic weakness, gains full control of HVAC systems — can modify temperature setpoints, disable alarms, or cause equipment damage.
Remediation	Update XWEB Pro firmware. … Detailed patch versions, workarounds, and compensating controls in full report.