What’s Vulnerable › Vulnerabilities

CVE-2021-33881

• Severity: medium (CVSS 4.2 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2021-06-06 · updated 2026-06-17
• Weakness: CWE-863

Description

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

• NXP Mifare Ultralight C Firmware: all versions
• NXP Mifare Ultralight Ev1 Firmware: all versions
• NXP Mifare Ultralight Nano Firmware: all versions
• NXP Ntag 210 Firmware: all versions
• NXP Ntag 212 Firmware: all versions
• NXP Ntag 213 Firmware: all versions
• NXP Ntag 215 Firmware: all versions
• NXP Ntag 216 Firmware: all versions

References

• https://blog.quarkslab.com/rfid-monotonic-counter-anti-tearing-defeated.html
• https://www.nxp.com/docs/en/application-note/AN11340.pdf
• https://www.nxp.com/docs/en/application-note/AN13089.pdf
• https://www.sstic.org/2021/presentation/eeprom_it_will_all_end_in_tears/
• https://blog.quarkslab.com/rfid-monotonic-counter-anti-tearing-defeated.html
• https://www.nxp.com/docs/en/application-note/AN11340.pdf
• https://www.nxp.com/docs/en/application-note/AN13089.pdf
• https://www.sstic.org/2021/presentation/eeprom_it_will_all_end_in_tears/

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