CVE-2026-84312: Nginx UI: Casdoor SSO callback uses a constant `state` parameter (login CSRF)

Summary

In the Casdoor SSO flow, the OAuth state parameter is hard-coded to settings.CasdoorSettings.Application — a value identical for every user and every login. The callback handler accepts whatever state the client sends without comparing it to anything stored in the user agent, enabling a login-CSRF: an attacker can force the victim's browser to authenticate as the attacker.

Details

api/user/casdoor.go:92-117 (GetCasdoorUri):

go func GetCasdoorUri(c gin.Context) { clientId := settings.CasdoorSettings.ClientId redirectUri := settings.CasdoorSettings.RedirectUri state := settings.CasdoorSettings.Application // ← constant ... c.JSON(http.StatusOK, gin.H{ "uri": fmt.Sprintf( "%s/login/oauth/authorize?clientid=%s&responsetype=code&redirecturi=%s&state=%s&scope=read", endpoint, clientId, encodedRedirectUri, state), }) }

api/user/casdoor.go:24-90 (CasdoorCallback):

go type CasdoorLoginUser struct { Code string json:"code" binding:"required,max=255" State string json:"state" binding:"required,max=255" }

func CasdoorCallback(c gin.Context) { var loginUser CasdoorLoginUser if !cosy.BindAndValid(c, &loginUser) { return } ... // state is NEVER compared to a per-session value token, err := casdoorsdk.GetOAuthToken(loginUser.Code, loginUser.State) ... u, err := user.GetUser(claims.Name) // username from Casdoor's JWT ... userToken, err := user.GenerateJWT(u) // JWT minted for whatever user came back }

Compare with the OIDC implementation in api/user/oidc.go:35-48, which generates a random state, stores it in an oidcstate cookie, and validates it on the callback. Casdoor has no such check.

Proof of Concept

1. Attacker initiates a Casdoor authorisation flow on their own browser, obtaining an authorisation code for their Casdoor account. 2. Attacker hosts a page that auto-submits the captured code to the victim's nginx-ui:

html <html><body><form action="https://victim.example/api/casdoorcallback" method="POST" enctype="text/plain" id="x"> <input name='{"code":"<attackercode>","state":"<App>","junk":"' value='"}'> </form> <script>document.getElementById('x').submit()</script> </body></html>

3. Server exchanges the attacker's code, looks up the username from claims.Name in the local user table, and mints a JWT for that row. The callback also sets the nginxuisecuresession cookie via middleware.EnsureSecureSessionCookie(c) (casdoor.go:84) — meaning the victim is now silently authenticated as the attacker. 4. Victim, believing they are using their own account, configures sites / TLS keys; the attacker reads them.

Impact

Login CSRF — the victim is forced to authenticate as the attacker, leading to data exfiltration of anything the victim subsequently uploads or configures. Particularly dangerous when nginx-ui is used by an organisation where Casdoor maps internal identities — the attacker can attribute their changes to the victim.

Patches

Mirror the OIDC implementation:

diff + import ( + "crypto/rand" + "crypto/subtle" + "encoding/hex" + ... + )

func GetCasdoorUri(c gin.Context) { ... - state := settings.CasdoorSettings.Application + b := make([]byte, 16) + if , err := rand.Read(b); err != nil { + cosy.ErrHandler(c, err); return + } + state := hex.EncodeToString(b) + c.SetSameSite(http.SameSiteLaxMode) + c.SetCookie("casdoorstate", state, 600, "/", "", + cSettings.ServerSettings.EnableHTTPS, true) ... }

func CasdoorCallback(c gin.Context) { + expected, err := c.Cookie("casdoorstate") + if err != nil { + c.AbortWithStatusJSON(http.StatusBadRequest, + gin.H{"message":"missing state cookie"}); return + } var loginUser CasdoorLoginUser if !cosy.BindAndValid(c, &loginUser) { return } + if subtle.ConstantTimeCompare([]byte(expected), []byte(loginUser.State)) != 1 { + c.AbortWithStatusJSON(http.StatusBadRequest, + gin.H{"message":"invalid state"}); return + } ... }

Workarounds

Disable Casdoor SSO until patched. The OIDC integration in api/user/oidc.go is correctly implemented and can be used as a substitute.

References

api/user/casdoor.go:92-117 api/user/casdoor.go:24-90 api/user/oidc.go:35-48 (correct implementation for comparison)

Credits

Vishal Shukla (@shukla304) and Sechub.dev AI Agent.