What is the CVSS score of CVE-2021-33881?

CVE-2021-33881 has a CVSS 3.1 base score of 4.2 (Medium). CVSS vector: CVSS:3.1/AV:P/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N. EPSS exploitation probability: 0.4%.

Is there a public PoC exploit available for CVE-2021-33881?

Yes, a public proof-of-concept exploit is available for CVE-2021-33881. Prioritise patching immediately. EPSS: 0.4%.

Mifare Ultralight Ev1 Firmware CVE-2021-33881

MEDIUM

Incorrect Authorization (CWE-863)

2021-06-06 cve@mitre.org

Authentication Bypass Mifare Ultralight Ev1 Firmware Mifare Ultralight C Firmware Mifare Ultralight Nano Firmware Ntag 210 Firmware Ntag 212 Firmware Ntag 213 Firmware Ntag 215 Firmware Ntag 216 Firmware Nxp

4.2

CVSS 3.1 · NVD

View

Vulnerability Assessment

Weakness	CWE CWE-863 OWASP Top 10:2025 A01:2025 - Broken Access Control ASVS 5.0 V8 - Authorization Authorization logic validation MITRE ATT&CK 1 technique across 1 tactic: Privilege Escalation The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. Sign in to read
Impact	CVSS score of 4.2 (MEDIUM). Attack characteristics: physical attack vector, high complexity, no privileges required, no user interaction not required. Public proof-of-concept exploit code is available.
Exploit ScenarioDerived	An attacker could exploit this vulnerability to bypass authorization checks to access restricted resources. No authentication is required to exploit this vulnerability.

This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).

No patch listed yet 0.4% exploitation probability (EPSS)

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AnalysisAI

On NXP MIFARE Ultralight and NTAG cards, an attacker can interrupt a write operation (aka conduct a "tear off" attack) over RFID to bypass a Monotonic Counter protection mechanism. Rated medium severity (CVSS 4.2), this vulnerability is no authentication required. Public exploit code available and no vendor patch available.

RemediationAI

No vendor patch is available at time of analysis. Monitor vendor advisories for updates. Review and test authorization logic, implement consistent access control checks, use centralized authorization framework.

Affects your stack

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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 as Incorrect Authorization (CWE-863), which allows attackers to bypass authorization checks to access restricted resources. On NXP MIFARE Ultralight and NTAG cards, an attacker can interrupt a write operation (aka conduct a "tear off" attack) over RFID to bypass a Monotonic Counter protection mechanism. The impact depends on how the anti tear-off feature is used in specific applications such as public transportation, physical access control, etc. Affected products include: Nxp Mifare Ultralight Ev1 Firmware, Nxp Mifare Ultralight C Firmware, Nxp Mifare Ultralight Nano Firmware, Nxp Ntag 210 Firmware, Nxp Ntag 212 Firmware.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 4.2 MEDIUM

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

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector

Physical

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

High

Availability

None

DescriptionNVD

On NXP MIFARE Ultralight and NTAG cards, an attacker can interrupt a write operation (aka conduct a "tear off" attack) over RFID to bypass a Monotonic Counter protection mechanism. The impact depends on how the anti tear-off feature is used in specific applications such as public transportation, physical access control, etc.

Threat Intelligence Overview

EPSS Score

0.4%

Top 67% exploitable

Exploit

POC

Public exploit code exists

Data Quality

2 sources

Confidence: Low

NVD

CVE.org

EPSS

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 MEDIUM

CISA KEV No

Public POC Yes

EPSS 0.4%

Patch available No

Active threat No

Deciding rule

MEDIUM severity (CVSS 4.0-6.9)

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.