# 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.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 21 Sep 2026
- **Updated:** 24 Sep 2026
- **Also known as:** GHSA-9xhm-w3wj-xhqh, GO-2026-6564

## 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 (Improper Restriction of Excessive Authentication Attempts)

## 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 | Ecosystem | 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.

## Is CVE-2026-77561 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-77561 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-77561 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-77561 exists.

Affected packages and fixed versions:
- github.com/tinyauthapp/tinyauth (Go): affected all versions; fixed in 1.0.1-0.20260715123057-dade1e2c8f27
- github.com/steveiliop56/tinyauth (Go): affected all versions; fixed in 1.0.1-0.20260715123057-dade1e2c8f27
- github.com/steveiliop56/tinyauth (Go): affected all versions; fixed in 1.0.1-0.20260715123057-dade1e2c8f27

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-2026-77561/ (Markdown: https://insights.sbomify.com/CVE-2026-77561/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-77561
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-77561
- OSV: https://osv.dev/vulnerability/CVE-2026-77561

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-77561/
Summaries are generated and may contain mistakes; the official description above is the record.