CVE-2026-77561: Brute Force (CVSS 5.3)

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.

Is your site exposed to CVE-2026-77561?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

5.3

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS — Exploit Prediction

0.0060

Probability of exploitation

0.47%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-307 CWE-307

References

Other References

https://github.com/tinyauthapp/tinyauth/commit/654b5cc436fc67865c1f55edf9ba9fbded50b74f https://github.com/tinyauthapp/tinyauth/commit/dade1e2c8f27a23df56ac216dcaf4b37081698e7 https://github.com/tinyauthapp/tinyauth/pull/1008 https://github.com/tinyauthapp/tinyauth/pull/943 https://github.com/tinyauthapp/tinyauth/releases/tag/v5.1.0 https://github.com/tinyauthapp/tinyauth/security/advisories/GHSA-9xhm-w3wj-xhqh https://github.com/tinyauthapp/tinyauth/security/advisories/GHSA-9xhm-w3wj-xhqh

Frequently Asked Questions

What is CVE-2026-77561? +

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. It has a CVSS v3.1 base score of 5.3 (MEDIUM).

How severe is CVE-2026-77561? +

CVE-2026-77561 has a CVSS v3.1 score of 5.3 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0060, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-77561? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2025-2911

Unauthorised access to the call forwarding service system in MeetMe products in versions prior to 2024-09 allows an attacker to …

CVE-2026-84461

Zammad is a web based open source helpdesk/customer support system. Prior to 7.1.2, the two-factor login step let an attacker …

CVE-2025-24806

Authelia is an open-source authentication and authorization server providing two-factor authentication and single sign-on (SSO) for applications via a web …

CVE-2025-1714

Lack of Rate Limiting in Sign-up workflow in Perforce Gliffy prior to version 4.14.0-7 on Gliffy online allows attacker to …

CVE-2025-0417

Lack of protection against brute force attacks in Valmet DNA visualization in DNA Operate. The possibility to make an arbitrary …

CVE-2025-42600

This vulnerability exists in Meon KYC solutions due to missing restrictions on the number of incorrect One-Time Password (OTP) attempts …

CVE-2026-77561