diff --git a/web/src/App.tsx b/web/src/App.tsx
index 9de74c605..b9569234e 100644
--- a/web/src/App.tsx
+++ b/web/src/App.tsx
@@ -4,6 +4,7 @@ import { useTranslation } from "react-i18next";
 import { Outlet } from "react-router-dom";
 import useNavigateTo from "./hooks/useNavigateTo";
 import { userStore, workspaceStore } from "./store";
+import { cleanupExpiredOAuthState } from "./utils/oauth";
 import { loadTheme } from "./utils/theme";
 
 const App = observer(() => {
@@ -13,6 +14,11 @@ const App = observer(() => {
   const userGeneralSetting = userStore.state.userGeneralSetting;
   const workspaceGeneralSetting = workspaceStore.state.generalSetting;
 
+  // Clean up expired OAuth states on app initialization
+  useEffect(() => {
+    cleanupExpiredOAuthState();
+  }, []);
+
   // Redirect to sign up page if no instance owner.
   useEffect(() => {
     if (!workspaceProfile.owner) {
diff --git a/web/src/pages/AuthCallback.tsx b/web/src/pages/AuthCallback.tsx
index 539750187..fc54b3897 100644
--- a/web/src/pages/AuthCallback.tsx
+++ b/web/src/pages/AuthCallback.tsx
@@ -1,4 +1,3 @@
-import { last } from "lodash-es";
 import { LoaderIcon } from "lucide-react";
 import { observer } from "mobx-react-lite";
 import { ClientError } from "nice-grpc-web";
@@ -8,6 +7,7 @@ import { authServiceClient } from "@/grpcweb";
 import { absolutifyLink } from "@/helpers/utils";
 import useNavigateTo from "@/hooks/useNavigateTo";
 import { initialUserStore } from "@/store/user";
+import { validateOAuthState } from "@/utils/oauth";
 
 interface State {
   loading: boolean;
@@ -29,21 +29,24 @@ const AuthCallback = observer(() => {
     if (!code || !state) {
       setState({
         loading: false,
-        errorMessage: "Failed to authorize. Invalid state passed to the auth callback.",
+        errorMessage: "Failed to authorize. Missing authorization code or state parameter.",
       });
       return;
     }
 
-    const identityProviderId = Number(last(state.split("-")));
-    if (!identityProviderId) {
+    // Validate OAuth state (CSRF protection)
+    const validatedState = validateOAuthState(state);
+    if (!validatedState) {
       setState({
         loading: false,
-        errorMessage: "No identity provider ID found in the state parameter.",
+        errorMessage: "Failed to authorize. Invalid or expired state parameter. This may indicate a CSRF attack attempt.",
       });
       return;
     }
 
+    const { identityProviderId, returnUrl } = validatedState;
     const redirectUri = absolutifyLink("/auth/callback");
+
     (async () => {
       try {
         await authServiceClient.createSession({
@@ -58,7 +61,8 @@ const AuthCallback = observer(() => {
           errorMessage: "",
         });
         await initialUserStore();
-        navigateTo("/");
+        // Redirect to return URL if specified, otherwise home
+        navigateTo(returnUrl || "/");
       } catch (error: any) {
         console.error(error);
         setState({
diff --git a/web/src/pages/SignIn.tsx b/web/src/pages/SignIn.tsx
index 00e968559..aa369f9cf 100644
--- a/web/src/pages/SignIn.tsx
+++ b/web/src/pages/SignIn.tsx
@@ -14,6 +14,7 @@ import { workspaceStore } from "@/store";
 import { extractIdentityProviderIdFromName } from "@/store/common";
 import { IdentityProvider, IdentityProvider_Type } from "@/types/proto/api/v1/idp_service";
 import { useTranslate } from "@/utils/i18n";
+import { storeOAuthState } from "@/utils/oauth";
 
 const SignIn = observer(() => {
   const t = useTranslate();
@@ -38,7 +39,6 @@ const SignIn = observer(() => {
   }, []);
 
   const handleSignInWithIdentityProvider = async (identityProvider: IdentityProvider) => {
-    const stateQueryParameter = `auth.signin.${identityProvider.title}-${extractIdentityProviderIdFromName(identityProvider.name)}`;
     if (identityProvider.type === IdentityProvider_Type.OAUTH2) {
       const redirectUri = absolutifyLink("/auth/callback");
       const oauth2Config = identityProvider.config?.oauth2Config;
@@ -46,12 +46,24 @@ const SignIn = observer(() => {
         toast.error("Identity provider configuration is invalid.");
         return;
       }
-      const authUrl = `${oauth2Config.authUrl}?client_id=${
-        oauth2Config.clientId
-      }&redirect_uri=${encodeURIComponent(redirectUri)}&state=${stateQueryParameter}&response_type=code&scope=${encodeURIComponent(
-        oauth2Config.scopes.join(" "),
-      )}`;
-      window.location.href = authUrl;
+
+      try {
+        // Generate and store secure state parameter with CSRF protection
+        const identityProviderId = extractIdentityProviderIdFromName(identityProvider.name);
+        const state = storeOAuthState(identityProviderId);
+
+        // Build OAuth authorization URL with secure state
+        const authUrl = `${oauth2Config.authUrl}?client_id=${
+          oauth2Config.clientId
+        }&redirect_uri=${encodeURIComponent(redirectUri)}&state=${state}&response_type=code&scope=${encodeURIComponent(
+          oauth2Config.scopes.join(" "),
+        )}`;
+
+        window.location.href = authUrl;
+      } catch (error) {
+        console.error("Failed to initiate OAuth flow:", error);
+        toast.error("Failed to initiate sign-in. Please try again.");
+      }
     }
   };
 
diff --git a/web/src/utils/oauth.ts b/web/src/utils/oauth.ts
new file mode 100644
index 000000000..045fddc82
--- /dev/null
+++ b/web/src/utils/oauth.ts
@@ -0,0 +1,111 @@
+/**
+ * OAuth state management utilities
+ * Implements secure state parameter handling following Auth0 best practices
+ * @see https://auth0.com/docs/secure/attack-protection/state-parameters
+ */
+
+const STATE_STORAGE_KEY = "oauth_state";
+const STATE_EXPIRY_MS = 10 * 60 * 1000; // 10 minutes
+
+interface OAuthState {
+  state: string;
+  identityProviderId: number;
+  timestamp: number;
+  returnUrl?: string;
+}
+
+/**
+ * Generate a cryptographically secure random state value
+ * Uses Web Crypto API for strong randomness
+ */
+function generateSecureState(): string {
+  const array = new Uint8Array(32);
+  crypto.getRandomValues(array);
+  return Array.from(array, (byte) => byte.toString(16).padStart(2, "0")).join("");
+}
+
+/**
+ * Store OAuth state in sessionStorage with metadata
+ * State is stored temporarily and will be validated on callback
+ */
+export function storeOAuthState(identityProviderId: number, returnUrl?: string): string {
+  const state = generateSecureState();
+  const stateData: OAuthState = {
+    state,
+    identityProviderId,
+    timestamp: Date.now(),
+    returnUrl,
+  };
+
+  try {
+    sessionStorage.setItem(STATE_STORAGE_KEY, JSON.stringify(stateData));
+  } catch (error) {
+    console.error("Failed to store OAuth state:", error);
+    throw new Error("Failed to initialize OAuth flow");
+  }
+
+  return state;
+}
+
+/**
+ * Validate and retrieve OAuth state from storage
+ * Implements CSRF protection by verifying state matches
+ * Cleans up expired or used states
+ */
+export function validateOAuthState(stateParam: string): { identityProviderId: number; returnUrl?: string } | null {
+  try {
+    const storedData = sessionStorage.getItem(STATE_STORAGE_KEY);
+    if (!storedData) {
+      console.error("No OAuth state found in storage");
+      return null;
+    }
+
+    const stateData: OAuthState = JSON.parse(storedData);
+
+    // Check if state has expired
+    if (Date.now() - stateData.timestamp > STATE_EXPIRY_MS) {
+      console.error("OAuth state has expired");
+      sessionStorage.removeItem(STATE_STORAGE_KEY);
+      return null;
+    }
+
+    // Validate state matches (CSRF protection)
+    if (stateData.state !== stateParam) {
+      console.error("OAuth state mismatch - possible CSRF attack");
+      sessionStorage.removeItem(STATE_STORAGE_KEY);
+      return null;
+    }
+
+    // State is valid, clean up and return data
+    sessionStorage.removeItem(STATE_STORAGE_KEY);
+    return {
+      identityProviderId: stateData.identityProviderId,
+      returnUrl: stateData.returnUrl,
+    };
+  } catch (error) {
+    console.error("Failed to validate OAuth state:", error);
+    sessionStorage.removeItem(STATE_STORAGE_KEY);
+    return null;
+  }
+}
+
+/**
+ * Clean up expired OAuth states
+ * Should be called on app initialization
+ */
+export function cleanupExpiredOAuthState(): void {
+  try {
+    const storedData = sessionStorage.getItem(STATE_STORAGE_KEY);
+    if (!storedData) {
+      return;
+    }
+
+    const stateData: OAuthState = JSON.parse(storedData);
+    if (Date.now() - stateData.timestamp > STATE_EXPIRY_MS) {
+      sessionStorage.removeItem(STATE_STORAGE_KEY);
+    }
+  } catch {
+    // If parsing fails, remove the corrupted data
+    sessionStorage.removeItem(STATE_STORAGE_KEY);
+  }
+}