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Fencer Vulns
medium 5.3

CVE-2026-77561 json

Tinyauth: Unauthenticated login attempts can trigger global login lockdown denial of service

published 2026-09-21 48 d ago modified 2026-10-01 38 d ago also GHSA-9xhm-w3wj-xhqh , GO-2026-6564 , EUVD-2026-84015

cvss
5.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 48%
public exploits
0
none known

Summary

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.

Patch / fix

  • go github.com/steveiliop56/tinyauth 1.0.1-0.20260715123057-dade1e2c8f27
  • go github.com/tinyauthapp/tinyauth 1.0.1-0.20260715123057-dade1e2c8f27

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
45 d ago

Exploit prediction

0.60% chance of exploitation in the next 30 days, higher than 48% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/tinyauthapp/tinyauth/security/advisories/GHSA-9xhm-w3wj-xhqh referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
GitHub 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Affected packages

ecosystem package affected fixed in
go github.com/steveiliop56/tinyauth
<1.0.1-0.20260715123057-dade1e2c8f27
1.0.1-0.20260715123057-dade1e2c8f27
go github.com/tinyauthapp/tinyauth
<1.0.1-0.20260715123057-dade1e2c8f27
1.0.1-0.20260715123057-dade1e2c8f27

Affected products

  • tinyauthapp tinyauth

Classification

Weakness
  • CWE-307 Improper Restriction of Excessive Authentication Attempts

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.