CVE-2026-33473 — api
MEDIUMCVE-2026-33473 is a medium-severity (CVSS 5.7) Improper Authentication vulnerability in code.vikunja.io/api. No vendor fix is recorded yet; mitigation options are listed below.
Vikunja has TOTP Reuse During Validity Window
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-33473.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-33473 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 379,145 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
code.vikunja.io/apiReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
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.
Similar CVEs
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | code.vikunja.io/api | ≥ 0.13 | No fix |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for code.vikunja.io/api, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Remediation status
No patched version of code.vikunja.io/api has shipped for CVE-2026-33473 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Mitigate without a patch
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-33473 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-33473. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-33473 in your dependencies?
O3 Security finds CVE-2026-33473 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.