Tinyauth: User enumeration attack by timing oracle

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Tinyauth is an authentication and authorization server. Prior to 5.1.0, Tinyauth exposes a remotely observable timing difference between authentication attempts for existing and nonexistent local usernames. internal/controller/user_controller.go loginHandler and internal/middleware/context_middleware.go basicAuth return quickly after internal/service/auth_service.go reports a missing user, while an existing user causes bcrypt password verification work. Repeated measurements can therefore disclose valid usernames and support targeted credential attacks. This issue is fixed in version 5.1.0.

Source published

21 Sep 2026 16:43:43 UTC

Source modified

23 Sep 2026 19:16:39 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 4.0 · 6.9 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

Tinyauth is an authentication and authorization server. Prior to 5.1.0, Tinyauth exposes a remotely observable timing difference between authentication attempts for existing and nonexistent local usernames. internal/controller/user_controller.go loginHandler and internal/middleware/context_middleware.go basicAuth return quickly after internal/service/auth_service.go reports a missing user, while an existing user causes bcrypt password verification work. Repeated measurements can therefore disclose valid usernames and support targeted credential attacks. This issue is fixed in version 5.1.0.

Source published

Sep 21, 2026, 4:43:43 PM (timezone not stated)

Source modified

Sep 23, 2026, 7:16:39 PM (timezone not stated)

Observed here

11 Nov 2026 16:09:07 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 4.0 · 6.9 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

Tinyauth is an authentication and authorization server. Prior to 5.1.0, Tinyauth exposes a remotely observable timing difference between authentication attempts for existing and nonexistent local usernames. internal/controller/user_controller.go loginHandler and internal/middleware/context_middleware.go basicAuth return quickly after internal/service/auth_service.go reports a missing user, while an existing user causes bcrypt password verification work. Repeated measurements can therefore disclose valid usernames and support targeted credential attacks. This issue is fixed in version 5.1.0.

Source published

21 Sep 2026 17:18:53 UTC

Source modified

30 Sep 2026 17:32:07 UTC

Observed here

25 Oct 2026 16:19:04 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 6.9 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

### Summary It's possible to enumerate users through a timing oracle. In other words: I can easily check if a username exists or not by observing the timing differences between logins. ### PoC Setup a tinyauth server with a local user. It can be over the network. Try to log in with the local user, using an incorrect password: there is a noticeable delay. You know that the user exists. Now try to log in with a username that does not exist, using an incorrect password: it will complete almost immediately. You know that the user does not exist. ### Expected vs actual behavior Login attempts should take roughly the same amount of time when the user exists vs when the user does not exist. Right now, nonexistent user attempts are way faster, meaning if your login attempt is slow, then the username exists for sure. ### Details Existing usernames will take an extra ~50 milliseconds to respond to login attempts, while non-existing usernames will take only ~50 microseconds (1000x less time) to return an incorrect password response. Even taking network traffic into consideration, it is trivial to check whether a local user exists or not. === Existing user, wrong password === #1: 50.52ms #2: 46.24ms #3: 43.57ms === Nonexistent user === #1: 43.03µs #2: 48.45µs #3: 59.33µs ### Suggested fix This can be solved by checking a dummy password hash when a user is not found before returning a query, this will mimic the exact same delay irrelevant of hardware capabilities. Potential patch: ``` From ca102773e0303f6025480efb26db379e3570a350 Mon Sep 17 00:00:00 2001 From: Disyer <[email protected]> Date: Tue, 14 Jul 2026 12:35:07 +0300 Subject: [PATCH] fix: prevent user enumeration by means of timing attack --- internal/controller/user_controller.go | 1 + internal/middleware/context_middleware.go | 1 + internal/service/auth_service.go | 10 ++++++++++ 3 files changed, 12 insertions(+) diff --git a/internal/controller/user_controller.go b/internal/controller/user_controller.go index ae6c23b..2ecc996 100644 --- a/internal/controller/user_controller.go +++ b/internal/controller/user_controller.go @@ -90,6 +90,7 @@ func (controller *UserController) loginHandler(c *gin.Context) { if err != nil { if errors.Is(err, service.ErrUserNotFound) { + controller.auth.DummyCheckPassword(req.Password) controller.log.App.Warn().Str("username", req.Username).Msg("User not found during login attempt") controller.auth.RecordLoginAttempt(req.Username, false) controller.log.AuditLoginFailure(req.Username, "unknown", c.ClientIP(), "user not found") diff --git a/internal/middleware/context_middleware.go b/internal/middleware/context_middleware.go index f49c85a..f70c9e7 100644 --- a/internal/middleware/context_middleware.go +++ b/internal/middleware/context_middleware.go @@ -244,6 +244,7 @@ func (m *ContextMiddleware) basicAuth(username string, password string) (*model. search, err := m.auth.SearchUser(username) if err != nil { + m.auth.DummyCheckPassword(password) return nil, nil, fmt.Errorf("error searching for user: %w", err) } diff --git a/internal/service/auth_service.go b/internal/service/auth_service.go index eeb5c8e..9cbc105 100644 --- a/internal/service/auth_service.go +++ b/internal/service/auth_service.go @@ -28,6 +28,10 @@ import ( const MaxOAuthPendingSessions = 256 const OAuthCleanupCount = 16 +// a dummy hash to check when a user is not found, to prevent user enumeration +// hardcoded to prevent having to generate a hash on every startup +const dummyHash = "$2a$10$iFQ6./j2a.UShYQOzWh4vOlnoze5DmHI3tRY3WU4YMj3zwp.t3TnO" + var ( ErrUserNotFound = errors.New("user not found") ) @@ -204,6 +208,12 @@ func (auth *AuthService) CheckUserPassword(search model.UserSearch, password str return errors.New("user authentication failed") } +func (auth *AuthService) DummyCheckPassword(password string) { + // When a user is not found, we still want to perform a password check to prevent + // timing attacks that could reveal whether a user exists or not + bcrypt.CompareHashAndPassword([]byte(dummyHash), []byte(password)) +} + func (auth *AuthService) GetLocalUser(username string) *model.LocalUser { if auth.runtime.LocalUsers == nil { return nil -- 2.55.0 ``` After testing the proposed fix, there is no discernible timing difference: === Existing user, wrong password === #1: 43.23ms #2: 43.26ms #3: 42.57ms === Nonexistent user === #1: 42.45ms #2: 42.11ms #3: 47.71ms

Source published

22 Sep 2026 20:37:06 UTC

Source modified

1 Oct 2026 20:56:17 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

Publisher rating · MODERATE

Tinyauth: User enumeration attack by timing oracle in github.com/tinyauthapp/tinyauth

Source published

1 Oct 2026 20:23:38 UTC

Source modified

1 Oct 2026 20:45:12 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.