CVE-2026-77561 Tinyauth: Unauthenticated login attempts can trigger global login lockdown denial of service
Unauthenticated attackers can trigger a global login lockdown in Tinyauth, denying service to valid users by exhausting login attempt records.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-77561?
CVE-2026-77561 is a medium-severity denial of service vulnerability in tinyauthapp tinyauth, published on 21 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Tinyauth is an authentication and authorization server. Prior to 5.1.0, an unauthenticated remote attacker can send POST /api/user/login requests with 257 distinct nonexistent usernames to fill MaxLoginAttemptRecords and activate a global login lockdown. internal/controller/user_controller.go loginHandler passes each attacker-controlled identifier to internal/service/auth_service.go RecordLoginAttempt, which invokes lockdownMode after the map reaches its cap. IsAccountLocked checks that global state before validating unrelated accounts, causing valid users to receive HTTP 429 until auth.loginTimeout expires, approximately 300 seconds by default. The attack can be repeated, but existing authenticated sessions are not invalidated. This issue is fixed in version 5.1.0.
Weakness: CWE-307
Which versions are affected by CVE-2026-77561?
3 open source packages ship an affected version, including github.com/tinyauthapp/tinyauth and github.com/steveiliop56/tinyauth.
| Package | Affected | Fixed in |
|---|---|---|
github.com/tinyauthapp/tinyauth Go | All versions | 1.0.1-0.20260715123057-dade1e2c8f27 |
github.com/steveiliop56/tinyauth Go | All versions | 1.0.1-0.20260715123057-dade1e2c8f27 |
github.com/steveiliop56/tinyauth Go | All versions | 1.0.1-0.20260715123057-dade1e2c8f27 |
How do I fix CVE-2026-77561?
Upgrade github.com/tinyauthapp/tinyauth to 1.0.1-0.20260715123057-dade1e2c8f27 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-77561 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-77561 exists.
Sources
Also known as GHSA-9xhm-w3wj-xhqh, GO-2026-6564.