GHSA-hf33-q6cf-c66f

### Summary Any user that has enabled the OTP 2FA can have their TOTP reused during the standard 30 second validity window.

### Details The https://github.com/pquerna/otp package [doesn't include](https://github.com/pquerna/otp/issues/61) checking for already used TOTPs within its the validity window. This requires each application that uses the package to implement their own method of tracking and verifying that codes can't be reused.

Section 6.5.1 within the [Authentication](https://github.com/OWASP/ASVS/blob/master/5.0/en/0x15-V6-Authentication.md) section of the OWASP ASVS recommends multiple checks, some of which involving TOTPs:

> Verify that lookup secrets, out-of-band authentication requests or codes, and time-based one-time passwords (TOTPs) are only successfully usable once.

The OWASP WSTG also references this as one of their [checks](https://owasp.org/www-project-web-security-testing-guide/latest/4-Web_Application_Security_Testing/04-Authentication_Testing/11-Testing_Multi-Factor_Authentication) to look for:

> Can the OTPs be used more than once?

### PoC

https://github.com/user-attachments/assets/86a43374-39bf-4d61-8f6d-5cc440c99a1e

### Impact Any user who uses 2FA could be impacted if their traffic is able to be captured, they're phished/social engineered, or other methods of attack. This disrupts one layer of the defense-in-depth model surrounding 2FA.

### Similar CVEs - [CVE-2025-6014](https://nvd.nist.gov/vuln/detail/CVE-2025-6014) - [CVE-2025-55003](https://nvd.nist.gov/vuln/detail/CVE-2025-55003) - [CVE-2026-33473](https://github.com/go-vikunja/vikunja/security/advisories/GHSA-p747-qc5p-773r)

### Remediation Store a deny-list of TOTP codes for their validity windows and check submitted codes against it to ensure none are being reused. After their validity window has closed, the 2FA code can be removed from the list.