Windows
CVE-2026-33473
MEDIUM
GHSA-p747-qc5p-773r
Severity by source
AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:N/A:N
Primary rating from GitHub Advisory.
CVSS VectorGitHub Advisory
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:N/A:N
Lifecycle Timeline
2DescriptionGitHub Advisory
Summary
Any user that has enabled 2FA can have their TOTP reused during the standard 30 second validity window.
Details
The below code is called when a user that has 2FA is authenticating to the application. Once they submit a valid username-password-totp combination, the user gets authenticated. If that same TOTP is used for the same user's account again within the validity window, it will allow the other session to authenticate successfully.
Source: <ins>pkg/user/totp.go:128</ins>
// ValidateTOTPPasscode validated totp codes of users.
func ValidateTOTPPasscode(s *xorm.Session, passcode *TOTPPasscode) (t *TOTP, err error) {
t, err = GetTOTPForUser(s, passcode.User)
if err != nil {
return
}
if !totp.Validate(passcode.Passcode, t.Secret) {
return nil, ErrInvalidTOTPPasscode{Passcode: passcode.Passcode}
}
return
}Section 6.5.1 within the Authentication 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 to look for:
> Can the OTPs be used more than once?
PoC
https://github.com/user-attachments/assets/19d3b4c3-c219-4f59-b57d-45c9f6a264c8
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.
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.
AnalysisAI
A time-based one-time password (TOTP) reuse vulnerability exists in Vikunja's authentication implementation where a valid TOTP code can be used multiple times within its 30-second validity window, allowing an attacker who captures or obtains a valid code to authenticate as a targeted user. This affects all users who have enabled two-factor authentication (2FA) on Vikunja instances, and while the CVSS score of 5.7 reflects moderate severity, the vulnerability undermines a critical layer of the defense-in-depth authentication model. A proof-of-concept demonstrating the reuse attack has been publicly disclosed.
Technical ContextAI
The vulnerability exists in the Vikunja API's TOTP validation function located in pkg/user/totp.go:128, which performs cryptographic validation of submitted passcodes against the user's TOTP secret but fails to implement a critical security control: preventing replay of valid codes within the TOTP time-step window. The affected product is identified via CPE as pkg:go/code.vikunja.io_api. The root cause is classified under CWE-287 (Improper Authentication) and specifically violates OWASP ASVS 6.5.1 and OWASP WSTG authentication testing guidelines, both of which explicitly require that time-based one-time passwords be usable only once. Unlike properly implemented TOTP systems that maintain a deny-list or used-code registry, Vikunja's ValidateTOTPPasscode function only validates the cryptographic correctness of the code without checking whether it has already been consumed.
RemediationAI
Upgrade Vikunja to a patched version that implements TOTP replay prevention as specified in the official GitHub security advisory (https://github.com/go-vikunja/vikunja/security/advisories/GHSA-p747-qc5p-773r). The upstream remediation involves implementing a deny-list or used-code registry to track TOTP codes that have been successfully validated during their 30-second validity window, ensuring each code can only be used once per user. Until a patch is available and deployed, temporarily disable 2FA for Vikunja instances if possible, enforce HTTPS-only connections to prevent traffic interception of authentication requests, and restrict administrative access to trusted networks. Instance administrators should immediately apply patches once released by the Vikunja project and advise all users to monitor their accounts for unauthorized access.
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Same weakness CWE-287 – Improper Authentication
View allSame technique Authentication Bypass
View allVendor StatusVendor
SUSE
Severity: Medium| Product | Status |
|---|---|
| openSUSE Leap 15.6 | Fixed |
| SUSE Linux Enterprise Module for Package Hub 15 SP5 | Fixed |
| SUSE Linux Enterprise Module for Package Hub 15 SP6 | Fixed |
| openSUSE Leap 15.5 | Fixed |
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External POC / Exploit Code
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