CVE-2026-42223: nginx-ui: Settings API Exposes Protected Secrets

Summary The GetSettings API handler (api/settings/settings.go:24-65) serializes all settings structs to JSON and returns them to authenticated users. Many sensitive fields are tagged with protected:"true" - however, this tag is only enforced during writes (via ProtectedFill in SaveSettings) and is completely ignored during reads. This exposes 40+ protected fields including JwtSecret (enabling auth token forgery), NodeSecret (enabling cluster node impersonation), OIDC ClientSecret (enabling OAuth account takeover), and the IP whitelist configuration.

Details Vulnerable Code

api/settings/settings.go:49-64 - GetSettings serializes all fields

go c.JSON(http.StatusOK, gin.H{ "app": cSettings.AppSettings, "server": cSettings.ServerSettings, "database": settings.DatabaseSettings, "auth": settings.AuthSettings, "casdoor": settings.CasdoorSettings, "oidc": settings.OIDCSettings, "cert": settings.CertSettings, "http": settings.HTTPSettings, "logrotate": settings.LogrotateSettings, "nginx": settings.NginxSettings, "node": settings.NodeSettings, "openai": settings.OpenAISettings, "terminal": settings.TerminalSettings, "webauthn": settings.WebAuthnSettings, })

Go's json.Marshal serializes all exported fields with json: tags. The protected:"true" struct tag is a custom tag - it has no effect on JSON serialization.

Protection is Write-Only

api/settings/settings.go:126-135 - ProtectedFill only used during saves

go cSettings.ProtectedFill(cSettings.AppSettings, &json.App) cSettings.ProtectedFill(cSettings.ServerSettings, &json.Server) cSettings.ProtectedFill(settings.AuthSettings, &json.Auth) // ... etc

ProtectedFill prevents overwriting protected fields during SaveSettings, but GetSettings has no corresponding filter. The protection is asymmetric - secrets can be read but not overwritten.

Exposed Protected Fields

settings/node.go: - Secret (protected) - used for cluster node authentication - SkipInstallation (protected), Demo (protected)

settings/oidc.go (all protected): - ClientId, ClientSecret, Endpoint, RedirectUri, Scopes, Identifier

settings/casdoor.go (all protected): - Endpoint, ExternalUrl, ClientId, ClientSecret, CertificatePath, Organization, Application, RedirectUri

settings/auth.go: - IPWhiteList (protected) - exposes security configuration

Attack Scenario

1. Low-privilege authenticated user calls GET /api/settings 2. Response includes NodeSecret - attacker can impersonate cluster nodes 3. Response includes OIDC ClientSecret - attacker can perform OAuth flows as the application 4. Response includes IPWhiteList - attacker learns network security configuration 5. If JwtSecret is in app settings (via cosy framework), attacker can forge authentication tokens for any user

PoC 1. GetSettings serializes all fields without filtering protected:"true" tags. From api/settings/settings.go:49-64:

go c.JSON(http.StatusOK, gin.H{ "app": cSettings.AppSettings, "server": cSettings.ServerSettings, "database": settings.DatabaseSettings, "auth": settings.AuthSettings, "casdoor": settings.CasdoorSettings, "oidc": settings.OIDCSettings, "cert": settings.CertSettings, "http": settings.HTTPSettings, "logrotate": settings.LogrotateSettings, "nginx": settings.NginxSettings, "node": settings.NodeSettings, "openai": settings.OpenAISettings, "terminal": settings.TerminalSettings, "webauthn": settings.WebAuthnSettings, })

Go's json.Marshal serializes all exported fields. The custom protected:"true" tag has no effect on serialization.

2. Protected secrets are defined across settings/.go. High-impact examples:

go // settings/serverv1.go:19 JwtSecret string json:"jwtsecret" protected:"true"

// settings/node.go:5 Secret string json:"secret" protected:"true"

// settings/oidc.go ClientSecret string json:"clientsecret" protected:"true"

// settings/auth.go IPWhiteList []string json:"ipwhitelist" protected:"true"

3. ProtectedFill is write-only. It appears 10 times in SaveSettings (lines 126-135) but 0 times in GetSettings:

go // api/settings/settings.go:126-135 - Only used during writes cSettings.ProtectedFill(cSettings.AppSettings, &json.App) cSettings.ProtectedFill(cSettings.ServerSettings, &json.Server) cSettings.ProtectedFill(settings.AuthSettings, &json.Auth) // ... 7 more calls

4. Exploit request. Any authenticated user can retrieve all secrets:

http GET /api/settings HTTP/1.1 Authorization: Bearer <any-valid-jwt>

Response includes (among 45 protected fields): json { "app": {"jwtsecret": "<the-actual-jwt-signing-key>", ...}, "node": {"secret": "<node-authentication-secret>", ...}, "oidc": {"clientsecret": "<oidc-client-secret>", ...}, "casdoor": {"clientsecret": "<casdoor-client-secret>", ...}, "auth": {"ipwhitelist": ["10.0.0.1", ...], ...}, "nginx": {"reloadcmd": "nginx -s reload", "restartcmd": "...", ...} }

Impact - Authentication bypass via JwtSecret: An attacker who obtains the JwtSecret can forge valid JWT tokens for any user, including admin accounts. This provides permanent, independent access that survives password changes and session revocations. - Cluster compromise via NodeSecret: The NodeSecret is used for inter-node authentication in nginx-ui clusters. An attacker can impersonate any cluster node, push malicious configurations to all nodes, and intercept cluster synchronization traffic. - Third-party OAuth takeover: Leaked OIDC ClientSecret and Casdoor ClientSecret allow the attacker to perform OAuth flows as the nginx-ui application, potentially gaining access to user accounts on the identity provider. - Security configuration disclosure: The IPWhiteList, ReloadCmd, RestartCmd, ConfigDir, SbinPath, and other protected fields reveal the security posture and infrastructure layout, enabling more targeted attacks. - Low barrier to exploitation: Any authenticated user (not just admins) can access GET /api/settings. In multi-user deployments, a low-privilege operator can escalate to full admin access.

Remediation

Filter out protected:"true" fields before serialization.