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CVE Record

CVE-2021-33881: On NXP MIFARE Ultralight and NTAG cards, an attacker can interrupt a write operation (aka conduct a "tear o...

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.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

This issue affects systems that rely on certain NXP RFID cards to maintain a trustworthy usage counter. An attacker near the card may interrupt a write operation and bypass the counter protection. Business impact depends entirely on the application, such as fare media, access badges, or other value/entitlement systems.

Executive priority

Treat this as an exposure-assessment priority, not an emergency patch event, unless the organization uses these cards for money, access, or safety-sensitive decisions.

Technical view

CVE-2021-33881 describes a tear-off attack against NXP MIFARE Ultralight and NTAG cards. By interrupting an RFID write operation, the monotonic counter anti-tearing mechanism can be bypassed. The source bundle provides no CVSS score, CWE, confirmed product version list, patch status, or active exploitation evidence.

Likely exposure

Exposure is likely limited to organizations using NXP MIFARE Ultralight or NTAG cards where application security depends on monotonic counters resisting interrupted writes.

Exploitation context

The CVE is not listed as KEV in the provided bundle. The public description supports a physical/RFID proximity attack model, but does not establish real-world exploitation, scale, or affected deployments.

Researcher notes

The strongest evidence is the described RFID tear-off bypass. The bundle lacks affected version granularity, vendor fix details, CVSS, and exploitation confirmation. Avoid broad claims beyond MIFARE Ultralight and NTAG deployments using monotonic counters.

Mitigation direction

  • Inventory deployments using NXP MIFARE Ultralight or NTAG cards.
  • Check NXP guidance and application notes for application-specific handling.
  • Do not rely solely on monotonic counters for critical entitlement decisions.
  • Ask card, reader, and application vendors for confirmed remediation guidance.
  • Prioritize review for transit, access-control, and stored-value use cases.

Validation and detection

  • Identify applications that use monotonic counters on affected card families.
  • Review whether interrupted writes could preserve value, access, or entitlement state.
  • Confirm card type and counter usage with the system integrator or vendor.
  • Check logs or reconciliation data for impossible counter or usage patterns.
  • Document whether compensating backend validation exists.
Prepared
Confidence
medium
Sources
6

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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CVE-2021-33881 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
5Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

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