diff --git a/api/controllers/openapi/oauth_device_sso.py b/api/controllers/openapi/oauth_device_sso.py
index 0218d143309..79538f48059 100644
--- a/api/controllers/openapi/oauth_device_sso.py
+++ b/api/controllers/openapi/oauth_device_sso.py
@@ -13,8 +13,10 @@ handlers do redirects + cookie kwargs that don't fit the Resource shape.
 from __future__ import annotations
 
 import logging
+import re
 import secrets
 from dataclasses import dataclass
+from urllib.parse import urlencode
 
 from flask import jsonify, make_response, redirect, request
 from pydantic import ValidationError
@@ -74,6 +76,21 @@ STATE_ENVELOPE_TTL_SECONDS = 15 * 60
 # Canonical sso-complete path. IdP-side ACS callback URL must point here.
 _SSO_COMPLETE_PATH = "/openapi/v1/oauth/device/sso-complete"
 
+_ALLOWED_SSO_ERRORS = {"sso_failed", "email_belongs_to_dify_account"}
+
+# user_code only ever reaches the redirect as a urlencoded query value; the
+# charset bound additionally forbids the path/scheme separators a redirection
+# attack would need, so an untrusted value cannot escape the fixed /device path.
+_USER_CODE_RE = re.compile(r"\A[A-Z0-9-]{1,16}\Z")
+
+
+def _device_error_redirect(code: str, user_code: str | None = None):
+    safe_code = code if code in _ALLOWED_SSO_ERRORS else "sso_failed"
+    params: dict[str, str] = {"sso_error": safe_code}
+    if user_code and _USER_CODE_RE.match(user_code):
+        params["user_code"] = user_code
+    return redirect(f"/device?{urlencode(params)}", code=302)
+
 
 def _trusted_origin() -> str:
     base = (dify_config.CONSOLE_API_URL or "").rstrip("/")
@@ -134,9 +151,21 @@ def sso_initiate():
 @bp.route("/oauth/device/sso-complete", methods=["GET"])
 @enterprise_only
 def sso_complete():
+    try:
+        return _sso_complete_impl()
+    except Exception:
+        logger.exception("sso-complete: unhandled")
+        return _device_error_redirect("sso_failed")
+
+
+def _sso_complete_impl():
+    inbound_error = request.args.get("sso_error")
+    if inbound_error:
+        return _device_error_redirect(inbound_error, request.args.get("user_code"))
+
     blob = request.args.get("sso_assertion")
     if not blob:
-        raise BadRequest("sso_assertion required")
+        return _device_error_redirect("sso_failed")
 
     keyset = jws.KeySet.from_shared_secret()
 
@@ -144,25 +173,26 @@ def sso_complete():
         raw_claims = jws.verify(keyset, blob, expected_aud=jws.AUD_EXT_SUBJECT_ASSERTION)
     except jws.VerifyError as e:
         logger.warning("sso-complete: rejected assertion: %s", e)
-        raise BadRequest("invalid_sso_assertion") from e
+        return _device_error_redirect("sso_failed")
 
     try:
         claims = ExtSubjectAssertionClaims.model_validate(raw_claims)
     except ValidationError as e:
         logger.warning("sso-complete: claim shape invalid: %s", e)
-        raise BadRequest("invalid_sso_assertion") from e
-
-    if not consume_sso_assertion_nonce(redis_client, claims.nonce):
-        raise BadRequest("invalid_sso_assertion")
+        return _device_error_redirect("sso_failed")
 
     user_code = claims.user_code.strip().upper()
+
+    if not consume_sso_assertion_nonce(redis_client, claims.nonce):
+        return _device_error_redirect("sso_failed", user_code)
+
     store = DeviceFlowRedis(redis_client)
     found = store.load_by_user_code(user_code)
     if found is None:
-        raise Conflict("user_code_not_pending")
+        return _device_error_redirect("sso_failed", user_code)
     _, state = found
     if state.status is not DeviceFlowStatus.PENDING:
-        raise Conflict("user_code_not_pending")
+        return _device_error_redirect("sso_failed", user_code)
 
     if AccountService.has_active_account_with_email(db.session, claims.email):
         _emit_external_rejection_audit(
@@ -170,7 +200,7 @@ def sso_complete():
             _RejectedClaims(subject_email=claims.email, subject_issuer=claims.issuer),
             reason="email_belongs_to_dify_account",
         )
-        return redirect("/device?sso_error=email_belongs_to_dify_account", code=302)
+        return _device_error_redirect("email_belongs_to_dify_account", user_code)
 
     iss = _trusted_origin()
     cookie_value, _ = mint_approval_grant(
diff --git a/api/tests/unit_tests/controllers/openapi/test_device_sso.py b/api/tests/unit_tests/controllers/openapi/test_device_sso.py
index 0125c583f04..655a5940f47 100644
--- a/api/tests/unit_tests/controllers/openapi/test_device_sso.py
+++ b/api/tests/unit_tests/controllers/openapi/test_device_sso.py
@@ -1,6 +1,7 @@
 """SSO-branch device-flow endpoints under /openapi/v1/oauth/device/."""
 
 import builtins
+from unittest.mock import MagicMock, patch
 
 import pytest
 from flask import Flask
@@ -77,3 +78,97 @@ def test_sso_complete_idp_callback_url_uses_canonical_path():
     from controllers.openapi import oauth_device_sso
 
     assert oauth_device_sso._SSO_COMPLETE_PATH == "/openapi/v1/oauth/device/sso-complete"
+
+
+# ---------------------------------------------------------------------------
+# _device_error_redirect helper
+# ---------------------------------------------------------------------------
+
+
+def test_device_error_redirect_builds_relative_location():
+    from controllers.openapi import oauth_device_sso
+
+    app = Flask(__name__)
+    with app.test_request_context():
+        resp = oauth_device_sso._device_error_redirect("sso_failed", "ABCD-1234")
+    assert resp.status_code == 302
+    loc = resp.headers["Location"]
+    assert loc.startswith("/device?")
+    assert "sso_error=sso_failed" in loc
+    assert "user_code=ABCD-1234" in loc
+
+
+def test_device_error_redirect_clamps_unknown_code():
+    from controllers.openapi import oauth_device_sso
+
+    app = Flask(__name__)
+    with app.test_request_context():
+        resp = oauth_device_sso._device_error_redirect("totally-bogus")
+    assert "sso_error=sso_failed" in resp.headers["Location"]
+
+
+def test_device_error_redirect_keeps_email_special_case():
+    from controllers.openapi import oauth_device_sso
+
+    app = Flask(__name__)
+    with app.test_request_context():
+        resp = oauth_device_sso._device_error_redirect("email_belongs_to_dify_account", "ABCD-1234")
+    assert "sso_error=email_belongs_to_dify_account" in resp.headers["Location"]
+
+
+def test_device_error_redirect_omits_empty_user_code():
+    from controllers.openapi import oauth_device_sso
+
+    app = Flask(__name__)
+    with app.test_request_context():
+        resp = oauth_device_sso._device_error_redirect("sso_failed")
+    assert "user_code=" not in resp.headers["Location"]
+
+
+def test_device_error_redirect_drops_malformed_user_code():
+    from controllers.openapi import oauth_device_sso
+
+    app = Flask(__name__)
+    with app.test_request_context():
+        resp = oauth_device_sso._device_error_redirect("sso_failed", "https://evil.example/")
+    loc = resp.headers["Location"]
+    assert loc.startswith("/device?")
+    assert "user_code=" not in loc
+    assert "evil" not in loc
+
+
+# ---------------------------------------------------------------------------
+# sso_complete redirect behaviour
+# ---------------------------------------------------------------------------
+
+
+def _ee_features():
+    from services.feature_service import LicenseStatus
+
+    m = MagicMock()
+    m.license.status = LicenseStatus.ACTIVE
+    return m
+
+
+@patch("libs.device_flow_security.FeatureService.get_system_features")
+def test_sso_complete_relays_inbound_sso_error(ee_feat, openapi_app):
+    ee_feat.return_value = _ee_features()
+    client = openapi_app.test_client()
+    resp = client.get(
+        "/openapi/v1/oauth/device/sso-complete?sso_error=sso_failed&user_code=ABCD-1234",
+        follow_redirects=False,
+    )
+    assert resp.status_code == 302
+    loc = resp.headers["Location"]
+    assert "/device?" in loc
+    assert "sso_error=sso_failed" in loc
+    assert "user_code=ABCD-1234" in loc
+
+
+@patch("libs.device_flow_security.FeatureService.get_system_features")
+def test_sso_complete_missing_assertion_redirects_generic(ee_feat, openapi_app):
+    ee_feat.return_value = _ee_features()
+    client = openapi_app.test_client()
+    resp = client.get("/openapi/v1/oauth/device/sso-complete", follow_redirects=False)
+    assert resp.status_code == 302
+    assert "sso_error=sso_failed" in resp.headers["Location"]
diff --git a/api/tests/unit_tests/controllers/openapi/test_oauth_sso_claims.py b/api/tests/unit_tests/controllers/openapi/test_oauth_sso_claims.py
index 9eb4cf01f41..9551a37142f 100644
--- a/api/tests/unit_tests/controllers/openapi/test_oauth_sso_claims.py
+++ b/api/tests/unit_tests/controllers/openapi/test_oauth_sso_claims.py
@@ -34,8 +34,9 @@ def test_sso_complete_rejects_assertion_missing_email(ee_feat, jws_mod, app: Fla
     jws_mod.VerifyError = Exception
 
     client = app.test_client()
-    resp = client.get("/openapi/v1/oauth/device/sso-complete?sso_assertion=blob")
-    assert resp.status_code == 400, resp.data
+    resp = client.get("/openapi/v1/oauth/device/sso-complete?sso_assertion=blob", follow_redirects=False)
+    assert resp.status_code == 302, resp.data
+    assert "sso_error=sso_failed" in resp.headers["Location"]
 
 
 @patch("controllers.openapi.oauth_device_sso.jws")
@@ -48,8 +49,9 @@ def test_sso_complete_rejects_assertion_empty_issuer(ee_feat, jws_mod, app: Flas
     jws_mod.VerifyError = Exception
 
     client = app.test_client()
-    resp = client.get("/openapi/v1/oauth/device/sso-complete?sso_assertion=blob")
-    assert resp.status_code == 400
+    resp = client.get("/openapi/v1/oauth/device/sso-complete?sso_assertion=blob", follow_redirects=False)
+    assert resp.status_code == 302
+    assert "sso_error=sso_failed" in resp.headers["Location"]
 
 
 def test_verify_approval_grant_raises_on_missing_field():
diff --git a/web/app/device/__tests__/page-terminal.spec.tsx b/web/app/device/__tests__/page-terminal.spec.tsx
index aba7b7391ac..e9fe1c0055a 100644
--- a/web/app/device/__tests__/page-terminal.spec.tsx
+++ b/web/app/device/__tests__/page-terminal.spec.tsx
@@ -121,40 +121,53 @@ describe('error_lookup_failed terminal state', () => {
   })
 })
 
-describe('sso_error inline banner on the code-entry page', () => {
-  const SSO_BANNER_COPY = 'deviceFlow.ssoError.emailBelongsToDifyAccount'
+describe('error_sso dedicated view', () => {
+  const TITLE = 'deviceFlow.errorSso.title'
+  const GENERIC = 'deviceFlow.ssoError.default'
+  const EMAIL_COPY = 'deviceFlow.ssoError.emailBelongsToDifyAccount'
+  const BACK_TO_LOGIN = 'deviceFlow.errorSso.backToLoginOptions'
 
-  it('shows the error banner with friendly copy when sso_error is present', async () => {
-    mockSearchParams = { sso_error: 'email_belongs_to_dify_account' }
+  it('renders the dedicated SSO error screen (not the code-entry page)', async () => {
+    mockSearchParams = { sso_error: 'sso_failed', user_code: 'ABCD-3456' }
     render(<DevicePage />)
-    expect(await screen.findByText(SSO_BANNER_COPY)).toBeInTheDocument()
+    expect(await screen.findByText(TITLE)).toBeInTheDocument()
+    expect(await screen.findByText(GENERIC)).toBeInTheDocument()
+    expect(screen.queryByRole('textbox')).not.toBeInTheDocument()
   })
 
-  it('keeps the code-entry screen visible (error on main page, not a separate view)', async () => {
-    mockSearchParams = { sso_error: 'email_belongs_to_dify_account' }
+  it('shows the email special-case copy', async () => {
+    mockSearchParams = { sso_error: 'email_belongs_to_dify_account', user_code: 'ABCD-3456' }
     render(<DevicePage />)
-    await screen.findByText(SSO_BANNER_COPY)
-    expect(screen.getByRole('textbox')).toBeInTheDocument()
-    expect(screen.getByRole('button', { name: /deviceFlow.codeEntry.continue/i })).toBeInTheDocument()
+    expect(await screen.findByText(EMAIL_COPY)).toBeInTheDocument()
   })
 
-  it('does not surface the raw backend error code', async () => {
-    mockSearchParams = { sso_error: 'email_belongs_to_dify_account' }
+  it('never surfaces the raw backend code', async () => {
+    mockSearchParams = { sso_error: 'email_belongs_to_dify_account', user_code: 'ABCD-3456' }
     render(<DevicePage />)
-    await screen.findByText(SSO_BANNER_COPY)
+    await screen.findByText(EMAIL_COPY)
     expect(screen.queryByText('email_belongs_to_dify_account')).not.toBeInTheDocument()
   })
 
-  it('does not scrub the param on mount (regression: error was wiped by router.replace)', async () => {
-    mockSearchParams = { sso_error: 'email_belongs_to_dify_account' }
+  it('scrubs sso_error + user_code from the URL on mount', async () => {
+    mockSearchParams = { sso_error: 'sso_failed', user_code: 'ABCD-3456' }
     render(<DevicePage />)
-    await screen.findByText(SSO_BANNER_COPY)
-    expect(mockReplace).not.toHaveBeenCalled()
+    await screen.findByText(TITLE)
+    expect(mockReplace).toHaveBeenCalledWith('/device')
   })
 
-  it('shows no banner when sso_error is absent', () => {
+  it('"Back to login options" re-checks the code and advances to the chooser', async () => {
+    mockSearchParams = { sso_error: 'sso_failed', user_code: 'ABCD-3456' }
+    mockDeviceLookup.mockResolvedValue({ valid: true })
+    render(<DevicePage />)
+    await screen.findByText(TITLE)
+    fireEvent.click(screen.getByRole('button', { name: BACK_TO_LOGIN }))
+    await screen.findByText('chooser.subtitle')
+    expect(mockDeviceLookup).toHaveBeenCalledWith('ABCD-3456')
+  })
+
+  it('shows no SSO error screen when sso_error is absent', () => {
     render(<DevicePage />)
     expect(screen.getByRole('textbox')).toBeInTheDocument()
-    expect(screen.queryByText(SSO_BANNER_COPY)).not.toBeInTheDocument()
+    expect(screen.queryByText(TITLE)).not.toBeInTheDocument()
   })
 })
diff --git a/web/app/device/page.tsx b/web/app/device/page.tsx
index 048d7e44ae5..75d0be64b76 100644
--- a/web/app/device/page.tsx
+++ b/web/app/device/page.tsx
@@ -26,6 +26,7 @@ type View
     | { kind: 'error_expired' }
     | { kind: 'error_rate_limited' }
     | { kind: 'error_lookup_failed' }
+    | { kind: 'error_sso', code: string, userCode: string }
 
 export default function DevicePage() {
   const { t } = useTranslation('deviceFlow')
@@ -74,6 +75,11 @@ export default function DevicePage() {
   useEffect(() => {
     if (view.kind !== 'code_entry' && view.kind !== 'chooser')
       return
+    if (ssoError) {
+      setView({ kind: 'error_sso', code: ssoError, userCode: urlUserCode }) // eslint-disable-line react/set-state-in-effect
+      router.replace(pathname)
+      return
+    }
     // Post-login bounce: chooser holds the typed code, account just loaded.
     // The URL was already scrubbed on the first effect run, so urlUserCode
     // is empty here — advance using the userCode stashed in view state.
@@ -95,13 +101,11 @@ export default function DevicePage() {
     }
     if (consumed && (urlUserCode || ssoVerified))
       router.replace(pathname)
-  }, [urlUserCode, ssoVerified, account, view, router, pathname])
+  }, [urlUserCode, ssoVerified, ssoError, account, view, router, pathname])
 
-  const onContinue = async () => {
-    if (!isValidUserCode(typed))
-      return
+  const advanceFromCode = async (code: string) => {
     try {
-      const reply = await deviceLookup(typed)
+      const reply = await deviceLookup(code)
       if (!reply.valid) {
         setView({ kind: 'error_expired' })
         return
@@ -118,20 +122,20 @@ export default function DevicePage() {
       return
     }
     if (account)
-      setView({ kind: 'authorize_account', userCode: typed })
-    else setView({ kind: 'chooser', userCode: typed })
+      setView({ kind: 'authorize_account', userCode: code })
+    else setView({ kind: 'chooser', userCode: code })
+  }
+
+  const onContinue = async () => {
+    if (!isValidUserCode(typed))
+      return
+    await advanceFromCode(typed)
   }
 
   return (
     <>
       {view.kind === 'code_entry' && (
         <div className="flex flex-col gap-5">
-          {ssoError && (
-            <div className="flex items-start gap-2 rounded-lg bg-state-destructive-hover p-3">
-              <span className="mt-0.5 i-ri-close-circle-line h-4 w-4 shrink-0 text-util-colors-red-red-600" />
-              <p className="text-sm text-text-destructive">{ssoErrorCopy(ssoError, t)}</p>
-            </div>
-          )}
           <div>
             <h1 className="text-2xl font-semibold text-text-primary">{t('codeEntry.title')}</h1>
             <p className="mt-2 text-sm text-text-secondary">
@@ -273,6 +277,31 @@ export default function DevicePage() {
         </div>
       )}
 
+      {view.kind === 'error_sso' && (
+        <div className="flex flex-col gap-1">
+          <div className="mb-2.5 flex h-[38px] w-[38px] items-center justify-center rounded-full bg-state-warning-hover">
+            <span aria-hidden="true" className="i-ri-error-warning-line h-[18px] w-[18px] text-util-colors-yellow-yellow-600" />
+          </div>
+          <h1 className="text-xl font-semibold text-text-primary">{t('errorSso.title')}</h1>
+          <p className="text-sm text-text-secondary">{ssoErrorCopy(view.code, t)}</p>
+          <Divider className="my-3" />
+          <Button
+            variant="primary"
+            size="large"
+            className="w-full"
+            onClick={() => {
+              setErrMsg(null)
+              if (view.userCode)
+                advanceFromCode(view.userCode)
+              else
+                setView({ kind: 'code_entry' })
+            }}
+          >
+            {t('errorSso.backToLoginOptions')}
+          </Button>
+        </div>
+      )}
+
       {errMsg && (
         <p className="mt-4 text-sm text-text-destructive">{errMsg}</p>
       )}
diff --git a/web/i18n/en-US/device-flow.json b/web/i18n/en-US/device-flow.json
index 662a9734b39..18a69ff2217 100644
--- a/web/i18n/en-US/device-flow.json
+++ b/web/i18n/en-US/device-flow.json
@@ -36,6 +36,8 @@
   "errorLookupFailed.title": "Could not verify the code",
   "errorRateLimited.body": "Wait a moment and try again.",
   "errorRateLimited.title": "Too many attempts",
+  "errorSso.backToLoginOptions": "← Back to login options",
+  "errorSso.title": "Sign-in could not be completed",
   "ssoError.default": "Single sign-on could not be completed. Try again.",
   "ssoError.emailBelongsToDifyAccount": "This identity is linked to a Dify account. Use “Sign in with Dify account” instead.",
   "success.goToConsole": "Go to Dify console →",