# CVE-2021-33881: Security feature bypass in n/a

> Attackers can bypass Monotonic Counter protections on NXP MIFARE Ultralight and NTAG cards by interrupting write operations via RFID tear-off attacks.

- **Severity:** Medium 4.2 (`CVSS:3.1/AV:P/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 6 Jun 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-ff8p-pfwc-wjf2

## What is CVE-2021-33881?

CVE-2021-33881 is a medium-severity vulnerability in n/a, published on 6 Jun 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official 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.

Weakness: CWE-863 (Incorrect Authorization)

## Which versions are affected by CVE-2021-33881?

It affects 8 products.


Products: Nxp Mifare Ultralight C Firmware, Nxp Mifare Ultralight Ev1 Firmware, Nxp Mifare Ultralight Nano Firmware, Nxp Ntag 210 Firmware, Nxp Ntag 212 Firmware, Nxp Ntag 213 Firmware, Nxp Ntag 215 Firmware, Nxp Ntag 216 Firmware.

## How do I fix CVE-2021-33881?

No fix has been published for CVE-2021-33881 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-33881 being exploited?

There is no known exploitation of CVE-2021-33881 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-33881 and fix it if it is affected.

What it is: CVE-2021-33881 is a medium-severity vulnerability in n/a, published on 6 Jun 2021. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-33881 in the wild and no public exploit code.

Affected product: n/a. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-33881/ (Markdown: https://insights.sbomify.com/CVE-2021-33881/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-33881
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-33881
- OSV: https://osv.dev/vulnerability/CVE-2021-33881

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-33881/
Summaries are generated and may contain mistakes; the official description above is the record.