diff --git a/internal/application/service/embed_webhook.go b/internal/application/service/embed_webhook.go
index 2f1b9d26e..85a8b3e8f 100644
--- a/internal/application/service/embed_webhook.go
+++ b/internal/application/service/embed_webhook.go
@@ -25,6 +25,13 @@ const embedWebhookTimeout = 5 * time.Second
 // ErrEmbedWebhookURLInvalid is returned when a webhook URL fails format or SSRF checks.
 var ErrEmbedWebhookURLInvalid = errors.New("invalid embed webhook URL")
 
+func newEmbedWebhookHTTPClient() *http.Client {
+	return secutils.NewSSRFSafeHTTPClient(secutils.SSRFSafeHTTPClientConfig{
+		Timeout:      embedWebhookTimeout,
+		MaxRedirects: 5,
+	})
+}
+
 // ValidateEmbedWebhookURL checks an optional outbound webhook URL. Empty is allowed.
 func ValidateEmbedWebhookURL(raw string) error {
 	trimmed := strings.TrimSpace(raw)
@@ -90,7 +97,7 @@ func DispatchEmbedWebhook(ch *types.EmbedChannel, eventType, sessionID string, p
 			_, _ = mac.Write(raw)
 			req.Header.Set("X-WeKnora-Signature", "sha256="+hex.EncodeToString(mac.Sum(nil)))
 		}
-		resp, err := http.DefaultClient.Do(req)
+		resp, err := newEmbedWebhookHTTPClient().Do(req)
 		if err != nil {
 			logger.Warnf(context.Background(), "[embed_webhook] dispatch %s failed: %v", eventType, err)
 			return
diff --git a/internal/application/service/embed_webhook_test.go b/internal/application/service/embed_webhook_test.go
index f67732ab5..7719433b8 100644
--- a/internal/application/service/embed_webhook_test.go
+++ b/internal/application/service/embed_webhook_test.go
@@ -1,6 +1,13 @@
 package service
 
-import "testing"
+import (
+	stderrors "errors"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	secutils "github.com/Tencent/WeKnora/internal/utils"
+)
 
 func TestValidateEmbedWebhookURL(t *testing.T) {
 	withSSRFWhitelist(t, "*.example.com,127.0.0.1")
@@ -33,3 +40,27 @@ func TestSignEmbedWebhookBody(t *testing.T) {
 		t.Fatal("signature not deterministic")
 	}
 }
+
+func TestEmbedWebhookHTTPClientBlocksRedirectToInternalURL(t *testing.T) {
+	withSSRFWhitelist(t, "127.0.0.1")
+
+	origin := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		http.Redirect(w, r, "http://169.254.169.254/latest/meta-data/", http.StatusFound)
+	}))
+	defer origin.Close()
+
+	req, err := http.NewRequest(http.MethodPost, origin.URL, nil)
+	if err != nil {
+		t.Fatalf("NewRequest: %v", err)
+	}
+	resp, err := newEmbedWebhookHTTPClient().Do(req)
+	if resp != nil && resp.Body != nil {
+		_ = resp.Body.Close()
+	}
+	if err == nil {
+		t.Fatal("expected redirect to link-local metadata endpoint to be blocked")
+	}
+	if !stderrors.Is(err, secutils.ErrSSRFRedirectBlocked) {
+		t.Fatalf("error = %v, want ErrSSRFRedirectBlocked", err)
+	}
+}
diff --git a/internal/application/service/user.go b/internal/application/service/user.go
index 4dbf7d329..670d85e8c 100644
--- a/internal/application/service/user.go
+++ b/internal/application/service/user.go
@@ -1051,6 +1051,39 @@ type oidcTokenResponse struct {
 	TokenType   string `json:"token_type"`
 }
 
+func newOIDCHTTPClient() *http.Client {
+	cfg := secutils.DefaultSSRFSafeHTTPClientConfig()
+	cfg.Timeout = 30 * time.Second
+	return secutils.NewSSRFSafeHTTPClient(cfg)
+}
+
+func validateOIDCEndpoint(label, endpoint string, required bool) error {
+	endpoint = strings.TrimSpace(endpoint)
+	if endpoint == "" {
+		if required {
+			return fmt.Errorf("OIDC %s endpoint is required", label)
+		}
+		return nil
+	}
+	if err := secutils.ValidateURLForSSRF(endpoint); err != nil {
+		return fmt.Errorf("OIDC %s endpoint failed SSRF validation: %w", label, err)
+	}
+	return nil
+}
+
+func validateOIDCEndpoints(cfg *config.OIDCAuthConfig) error {
+	if err := validateOIDCEndpoint("authorization", cfg.AuthorizationEndpoint, true); err != nil {
+		return err
+	}
+	if err := validateOIDCEndpoint("token", cfg.TokenEndpoint, true); err != nil {
+		return err
+	}
+	if err := validateOIDCEndpoint("userinfo", cfg.UserInfoEndpoint, false); err != nil {
+		return err
+	}
+	return nil
+}
+
 func (s *userService) getOIDCConfig(ctx context.Context) (*config.OIDCAuthConfig, error) {
 	if s.config == nil || s.config.OIDCAuth == nil || !s.config.OIDCAuth.Enable {
 		return nil, errors.New("OIDC login is disabled")
@@ -1067,18 +1100,21 @@ func (s *userService) getOIDCConfig(ctx context.Context) (*config.OIDCAuthConfig
 
 func (s *userService) populateOIDCEndpoints(ctx context.Context, cfg *config.OIDCAuthConfig) error {
 	if strings.TrimSpace(cfg.AuthorizationEndpoint) != "" && strings.TrimSpace(cfg.TokenEndpoint) != "" {
-		return nil
+		return validateOIDCEndpoints(cfg)
 	}
 	if strings.TrimSpace(cfg.DiscoveryURL) == "" {
 		return errors.New("OIDC discovery_url or explicit endpoints are required")
 	}
+	if err := validateOIDCEndpoint("discovery", cfg.DiscoveryURL, true); err != nil {
+		return err
+	}
 
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, cfg.DiscoveryURL, nil)
 	if err != nil {
 		return fmt.Errorf("failed to create OIDC discovery request: %w", err)
 	}
 
-	resp, err := http.DefaultClient.Do(req)
+	resp, err := newOIDCHTTPClient().Do(req)
 	if err != nil {
 		return fmt.Errorf("failed to load OIDC discovery document: %w", err)
 	}
@@ -1104,10 +1140,14 @@ func (s *userService) populateOIDCEndpoints(ctx context.Context, cfg *config.OID
 	if cfg.AuthorizationEndpoint == "" || cfg.TokenEndpoint == "" {
 		return errors.New("OIDC discovery document missing required endpoints")
 	}
-	return nil
+	return validateOIDCEndpoints(cfg)
 }
 
 func (s *userService) exchangeOIDCCode(ctx context.Context, cfg *config.OIDCAuthConfig, code, redirectURI string) (*oidcTokenResponse, error) {
+	if err := validateOIDCEndpoint("token", cfg.TokenEndpoint, true); err != nil {
+		return nil, err
+	}
+
 	form := url.Values{}
 	form.Set("grant_type", "authorization_code")
 	form.Set("code", code)
@@ -1122,14 +1162,14 @@ func (s *userService) exchangeOIDCCode(ctx context.Context, cfg *config.OIDCAuth
 	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
 	req.Header.Set("Accept", "application/json")
 
-	resp, err := http.DefaultClient.Do(req)
+	resp, err := newOIDCHTTPClient().Do(req)
 	if err != nil {
 		return nil, fmt.Errorf("failed to exchange OIDC code: %w", err)
 	}
 	defer resp.Body.Close()
 	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
-		body, _ := io.ReadAll(io.LimitReader(resp.Body, 2048))
-		return nil, fmt.Errorf("OIDC token exchange failed: status=%d body=%s", resp.StatusCode, strings.TrimSpace(string(body)))
+		_, _ = io.Copy(io.Discard, io.LimitReader(resp.Body, 2048))
+		return nil, fmt.Errorf("OIDC token exchange failed: status=%d", resp.StatusCode)
 	}
 
 	var tokenResp oidcTokenResponse
@@ -1186,6 +1226,10 @@ func (s *userService) resolveOIDCUserInfo(ctx context.Context, cfg *config.OIDCA
 }
 
 func (s *userService) fetchOIDCUserInfo(ctx context.Context, endpoint, accessToken string) (map[string]interface{}, error) {
+	if err := validateOIDCEndpoint("userinfo", endpoint, true); err != nil {
+		return nil, err
+	}
+
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
 	if err != nil {
 		return nil, err
@@ -1193,14 +1237,14 @@ func (s *userService) fetchOIDCUserInfo(ctx context.Context, endpoint, accessTok
 	req.Header.Set("Authorization", "Bearer "+accessToken)
 	req.Header.Set("Accept", "application/json")
 
-	resp, err := http.DefaultClient.Do(req)
+	resp, err := newOIDCHTTPClient().Do(req)
 	if err != nil {
 		return nil, err
 	}
 	defer resp.Body.Close()
 	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
-		body, _ := io.ReadAll(io.LimitReader(resp.Body, 2048))
-		return nil, fmt.Errorf("userinfo request failed: status=%d body=%s", resp.StatusCode, strings.TrimSpace(string(body)))
+		_, _ = io.Copy(io.Discard, io.LimitReader(resp.Body, 2048))
+		return nil, fmt.Errorf("userinfo request failed: status=%d", resp.StatusCode)
 	}
 
 	var claims map[string]interface{}
diff --git a/internal/application/service/user_oidc_security_test.go b/internal/application/service/user_oidc_security_test.go
new file mode 100644
index 000000000..1ed336d1b
--- /dev/null
+++ b/internal/application/service/user_oidc_security_test.go
@@ -0,0 +1,87 @@
+package service
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/Tencent/WeKnora/internal/config"
+	secutils "github.com/Tencent/WeKnora/internal/utils"
+)
+
+func withOIDCSSRFWhitelist(t *testing.T, raw string) {
+	t.Helper()
+	t.Setenv("SSRF_WHITELIST", raw)
+	secutils.ResetSSRFWhitelistForTest()
+	t.Cleanup(secutils.ResetSSRFWhitelistForTest)
+}
+
+func TestOIDCDiscoveryRejectsInternalDiscoveredEndpoint(t *testing.T) {
+	withOIDCSSRFWhitelist(t, "127.0.0.1")
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_ = json.NewEncoder(w).Encode(oidcDiscoveryDocument{
+			AuthorizationEndpoint: serverURL(r, "/authorize"),
+			TokenEndpoint:         "http://169.254.169.254/latest/meta-data/",
+		})
+	}))
+	defer server.Close()
+
+	svc := &userService{}
+	cfg := &config.OIDCAuthConfig{DiscoveryURL: server.URL}
+	err := svc.populateOIDCEndpoints(context.Background(), cfg)
+	if err == nil || !strings.Contains(err.Error(), "OIDC token endpoint failed SSRF validation") {
+		t.Fatalf("populateOIDCEndpoints error = %v, want token SSRF validation failure", err)
+	}
+}
+
+func TestOIDCTokenExchangeBlocksRedirectToInternalURL(t *testing.T) {
+	withOIDCSSRFWhitelist(t, "127.0.0.1")
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		http.Redirect(w, r, "http://169.254.169.254/latest/meta-data/", http.StatusFound)
+	}))
+	defer server.Close()
+
+	svc := &userService{}
+	cfg := &config.OIDCAuthConfig{TokenEndpoint: server.URL, ClientID: "client-id", ClientSecret: "client-secret"}
+	_, err := svc.exchangeOIDCCode(context.Background(), cfg, "code", "https://app.example/callback")
+	if err == nil || !strings.Contains(err.Error(), secutils.ErrSSRFRedirectBlocked.Error()) {
+		t.Fatalf("exchangeOIDCCode error = %v, want redirect SSRF block", err)
+	}
+}
+
+func TestOIDCErrorsDoNotEchoSecrets(t *testing.T) {
+	withOIDCSSRFWhitelist(t, "127.0.0.1")
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusBadRequest)
+		_, _ = w.Write([]byte("client-secret bearer-token"))
+	}))
+	defer server.Close()
+
+	svc := &userService{}
+	cfg := &config.OIDCAuthConfig{TokenEndpoint: server.URL, ClientID: "client-id", ClientSecret: "client-secret"}
+	_, err := svc.exchangeOIDCCode(context.Background(), cfg, "code", "https://app.example/callback")
+	if err == nil {
+		t.Fatalf("exchangeOIDCCode returned nil error")
+	}
+	if strings.Contains(err.Error(), "client-secret") {
+		t.Fatalf("exchangeOIDCCode error leaked secret: %v", err)
+	}
+
+	_, err = svc.fetchOIDCUserInfo(context.Background(), server.URL, "bearer-token")
+	if err == nil {
+		t.Fatalf("fetchOIDCUserInfo returned nil error")
+	}
+	if strings.Contains(err.Error(), "bearer-token") {
+		t.Fatalf("fetchOIDCUserInfo error leaked bearer token: %v", err)
+	}
+}
+
+func serverURL(r *http.Request, path string) string {
+	return "http://" + r.Host + path
+}
diff --git a/internal/handler/knowledge.go b/internal/handler/knowledge.go
index 591918283..fc840dac9 100644
--- a/internal/handler/knowledge.go
+++ b/internal/handler/knowledge.go
@@ -1267,49 +1267,8 @@ func (h *KnowledgeHandler) DownloadKnowledgeFile(c *gin.Context) {
 
 // mimeTypeByExt returns the MIME type for a given file extension.
 func mimeTypeByExt(filename string) string {
-	ext := strings.ToLower(filename)
-	if idx := strings.LastIndex(ext, "."); idx >= 0 {
-		ext = ext[idx:]
-	} else {
-		ext = ""
-	}
-	m := map[string]string{
-		".pdf":      "application/pdf",
-		".docx":     "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
-		".doc":      "application/msword",
-		".pptx":     "application/vnd.openxmlformats-officedocument.presentationml.presentation",
-		".ppt":      "application/vnd.ms-powerpoint",
-		".xlsx":     "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
-		".xls":      "application/vnd.ms-excel",
-		".csv":      "text/csv",
-		".jpg":      "image/jpeg",
-		".jpeg":     "image/jpeg",
-		".png":      "image/png",
-		".gif":      "image/gif",
-		".bmp":      "image/bmp",
-		".webp":     "image/webp",
-		".svg":      "image/svg+xml",
-		".tiff":     "image/tiff",
-		".txt":      "text/plain; charset=utf-8",
-		".md":       "text/markdown; charset=utf-8",
-		".markdown": "text/markdown; charset=utf-8",
-		".json":     "application/json; charset=utf-8",
-		".xml":      "application/xml; charset=utf-8",
-		".html":     "text/html; charset=utf-8",
-		".css":      "text/css; charset=utf-8",
-		".js":       "text/javascript; charset=utf-8",
-		".ts":       "text/typescript; charset=utf-8",
-		".py":       "text/x-python; charset=utf-8",
-		".go":       "text/x-go; charset=utf-8",
-		".java":     "text/x-java; charset=utf-8",
-		".yaml":     "text/yaml; charset=utf-8",
-		".yml":      "text/yaml; charset=utf-8",
-		".sh":       "text/x-shellscript; charset=utf-8",
-	}
-	if ct, ok := m[ext]; ok {
-		return ct
-	}
-	return "application/octet-stream"
+	ct, _ := secutils.SafeContentTypeByFilename(filename)
+	return ct
 }
 
 // PreviewKnowledgeFile godoc
@@ -1347,9 +1306,14 @@ func (h *KnowledgeHandler) PreviewKnowledgeFile(c *gin.Context) {
 	}
 	defer file.Close()
 
-	contentType := mimeTypeByExt(filename)
+	contentType, inline := secutils.SafeContentTypeByFilename(filename)
 	c.Header("Content-Type", contentType)
-	c.Header("Content-Disposition", mime.FormatMediaType("inline", map[string]string{"filename": filename}))
+	c.Header("X-Content-Type-Options", "nosniff")
+	disposition := "inline"
+	if !inline {
+		disposition = "attachment"
+	}
+	c.Header("Content-Disposition", mime.FormatMediaType(disposition, map[string]string{"filename": filename}))
 	c.Header("Cache-Control", "private, max-age=3600")
 
 	c.Stream(func(w io.Writer) bool {
diff --git a/internal/handler/knowledge_preview_security_test.go b/internal/handler/knowledge_preview_security_test.go
new file mode 100644
index 000000000..972e818c5
--- /dev/null
+++ b/internal/handler/knowledge_preview_security_test.go
@@ -0,0 +1,67 @@
+package handler
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/Tencent/WeKnora/internal/middleware"
+	"github.com/Tencent/WeKnora/internal/types"
+	"github.com/Tencent/WeKnora/internal/types/interfaces"
+	"github.com/gin-gonic/gin"
+)
+
+type previewKnowledgeServiceStub struct {
+	interfaces.KnowledgeService
+	filename string
+}
+
+type closeNotifyRecorder struct {
+	*httptest.ResponseRecorder
+}
+
+func (r *closeNotifyRecorder) CloseNotify() <-chan bool {
+	ch := make(chan bool, 1)
+	return ch
+}
+
+func (s *previewKnowledgeServiceStub) GetKnowledgeByIDOnly(context.Context, string) (*types.Knowledge, error) {
+	return &types.Knowledge{ID: "k1", TenantID: 42, KnowledgeBaseID: "kb1"}, nil
+}
+
+func (s *previewKnowledgeServiceStub) GetKnowledgeFile(context.Context, string) (io.ReadCloser, string, error) {
+	return io.NopCloser(strings.NewReader(`<html><script>alert(1)</script></html>`)), s.filename, nil
+}
+
+func TestPreviewKnowledgeFileForcesActiveContentDownload(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	router := gin.New()
+	router.Use(middleware.ErrorHandler())
+	router.Use(func(c *gin.Context) {
+		c.Set(types.TenantIDContextKey.String(), uint64(42))
+		c.Next()
+	})
+
+	h := &KnowledgeHandler{kgService: &previewKnowledgeServiceStub{filename: "payload.html"}}
+	router.GET("/knowledge/:id/preview", h.PreviewKnowledgeFile)
+
+	req := httptest.NewRequest(http.MethodGet, "/knowledge/k1/preview", nil)
+	w := &closeNotifyRecorder{ResponseRecorder: httptest.NewRecorder()}
+	router.ServeHTTP(w, req)
+
+	if got, want := w.Code, http.StatusOK; got != want {
+		t.Fatalf("status = %d, want %d; body=%s", got, want, w.Body.String())
+	}
+	if got := w.Header().Get("Content-Type"); got != "application/octet-stream" {
+		t.Fatalf("Content-Type = %q, want application/octet-stream", got)
+	}
+	if got := w.Header().Get("X-Content-Type-Options"); got != "nosniff" {
+		t.Fatalf("X-Content-Type-Options = %q, want nosniff", got)
+	}
+	if got := w.Header().Get("Content-Disposition"); !strings.HasPrefix(got, "attachment") {
+		t.Fatalf("Content-Disposition = %q, want attachment", got)
+	}
+}
diff --git a/internal/im/mattermost/adapter_test.go b/internal/im/mattermost/adapter_test.go
index dc551cda3..d2ec460a3 100644
--- a/internal/im/mattermost/adapter_test.go
+++ b/internal/im/mattermost/adapter_test.go
@@ -1,16 +1,29 @@
 package mattermost
 
 import (
+	"context"
 	"encoding/json"
+	stderrors "errors"
+	"net/http"
+	"net/http/httptest"
 	"testing"
+
+	secutils "github.com/Tencent/WeKnora/internal/utils"
 )
 
+func withMattermostSSRFWhitelist(t *testing.T, whitelist string) {
+	t.Helper()
+	t.Setenv("SSRF_WHITELIST", whitelist)
+	secutils.ResetSSRFWhitelistForTest()
+	t.Cleanup(secutils.ResetSSRFWhitelistForTest)
+}
+
 func TestParseOutgoingBody_ThreadRoot(t *testing.T) {
 	tests := []struct {
-		name           string
-		payload        outgoingPayload
+		name            string
+		payload         outgoingPayload
 		postReplyToMain bool
-		wantThreadRoot string
+		wantThreadRoot  string
 	}{
 		{
 			name: "threaded reply has RootID",
@@ -60,6 +73,35 @@ func TestParseOutgoingBody_ThreadRoot(t *testing.T) {
 	}
 }
 
+func TestNewClientRejectsPrivateSiteURL(t *testing.T) {
+	withMattermostSSRFWhitelist(t, "")
+
+	if _, err := NewClient("http://127.0.0.1:8065", "bot-token"); err == nil {
+		t.Fatal("expected private Mattermost site_url to be rejected")
+	}
+}
+
+func TestMattermostClientBlocksRedirectToInternalURL(t *testing.T) {
+	withMattermostSSRFWhitelist(t, "127.0.0.1")
+
+	origin := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		http.Redirect(w, r, "http://169.254.169.254/latest/meta-data/", http.StatusFound)
+	}))
+	defer origin.Close()
+
+	client, err := NewClient(origin.URL, "bot-token")
+	if err != nil {
+		t.Fatalf("NewClient: %v", err)
+	}
+	_, err = client.CreatePost(context.Background(), "channel", "", "hello")
+	if err == nil {
+		t.Fatal("expected redirect to link-local metadata endpoint to be blocked")
+	}
+	if !stderrors.Is(err, secutils.ErrSSRFRedirectBlocked) {
+		t.Fatalf("error = %v, want ErrSSRFRedirectBlocked", err)
+	}
+}
+
 func TestParseOutgoingBody_JSON(t *testing.T) {
 	body := `{"token":"tok","user_id":"u1","user_name":"alice","channel_id":"ch1","post_id":"p1","text":"hello","root_id":"r1"}`
 
diff --git a/internal/im/mattermost/client.go b/internal/im/mattermost/client.go
index 501c3d749..a2727363e 100644
--- a/internal/im/mattermost/client.go
+++ b/internal/im/mattermost/client.go
@@ -7,8 +7,11 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"net/url"
 	"strings"
 	"time"
+
+	secutils "github.com/Tencent/WeKnora/internal/utils"
 )
 
 // Client calls Mattermost REST API v4.
@@ -25,14 +28,28 @@ func NewClient(siteURL, botToken string) (*Client, error) {
 	if siteURL == "" {
 		return nil, fmt.Errorf("site_url is required")
 	}
+	parsed, err := url.Parse(siteURL)
+	if err != nil || parsed.Host == "" {
+		return nil, fmt.Errorf("invalid site_url: must be a valid http(s) URL")
+	}
+	if parsed.Scheme != "http" && parsed.Scheme != "https" {
+		return nil, fmt.Errorf("invalid site_url: must use http or https")
+	}
+	if err := secutils.ValidateURLForSSRF(siteURL); err != nil {
+		return nil, fmt.Errorf(
+			"invalid site_url: %w (for private Mattermost deployments, add the hostname to SSRF_WHITELIST)",
+			err,
+		)
+	}
 	if strings.TrimSpace(botToken) == "" {
 		return nil, fmt.Errorf("bot_token is required")
 	}
 	return &Client{
 		baseURL: siteURL + "/api/v4",
-		httpClient: &http.Client{
-			Timeout: 60 * time.Second,
-		},
+		httpClient: secutils.NewSSRFSafeHTTPClient(secutils.SSRFSafeHTTPClientConfig{
+			Timeout:      60 * time.Second,
+			MaxRedirects: 5,
+		}),
 		token: strings.TrimSpace(botToken),
 	}, nil
 }
diff --git a/internal/im/qqbot/adapter_test.go b/internal/im/qqbot/adapter_test.go
index 288973294..f2902d23d 100644
--- a/internal/im/qqbot/adapter_test.go
+++ b/internal/im/qqbot/adapter_test.go
@@ -5,8 +5,16 @@ import (
 	"testing"
 
 	"github.com/Tencent/WeKnora/internal/im"
+	secutils "github.com/Tencent/WeKnora/internal/utils"
 )
 
+func withQQBotSSRFWhitelist(t *testing.T, whitelist string) {
+	t.Helper()
+	t.Setenv("SSRF_WHITELIST", whitelist)
+	secutils.ResetSSRFWhitelistForTest()
+	t.Cleanup(secutils.ResetSSRFWhitelistForTest)
+}
+
 func TestParseGatewayPayloadC2CMessage(t *testing.T) {
 	event := messageEvent{
 		ID:      "msg-1",
@@ -76,3 +84,27 @@ func TestParseExpiresIn(t *testing.T) {
 		})
 	}
 }
+
+func TestNewClientRejectsPrivateAPIBaseURL(t *testing.T) {
+	withQQBotSSRFWhitelist(t, "")
+
+	if _, err := NewClient("app", "secret", "http://127.0.0.1:8080", ""); err == nil {
+		t.Fatal("expected private qqbot api_base_url to be rejected")
+	}
+}
+
+func TestNewClientRejectsInsecureGatewayURL(t *testing.T) {
+	withQQBotSSRFWhitelist(t, "127.0.0.1")
+
+	if _, err := NewClient("app", "secret", "http://127.0.0.1:8080", "ws://127.0.0.1/gateway"); err == nil {
+		t.Fatal("expected non-wss qqbot gateway_url to be rejected")
+	}
+}
+
+func TestNewClientAllowsWhitelistedPrivateDeployment(t *testing.T) {
+	withQQBotSSRFWhitelist(t, "127.0.0.1")
+
+	if _, err := NewClient("app", "secret", "http://127.0.0.1:8080", "wss://127.0.0.1/gateway"); err != nil {
+		t.Fatalf("expected whitelisted private qqbot endpoints to pass: %v", err)
+	}
+}
diff --git a/internal/im/qqbot/client.go b/internal/im/qqbot/client.go
index 49ebc3ed7..ce8c41b58 100644
--- a/internal/im/qqbot/client.go
+++ b/internal/im/qqbot/client.go
@@ -6,9 +6,12 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/http"
+	"net/url"
 	"strings"
 	"sync"
 	"time"
+
+	secutils "github.com/Tencent/WeKnora/internal/utils"
 )
 
 type Client struct {
@@ -35,12 +38,23 @@ func NewClient(appID, clientSecret, apiBaseURL, gatewayURL string) (*Client, err
 	if apiBaseURL == "" {
 		apiBaseURL = defaultAPIBaseURL
 	}
+	apiBaseURL = strings.TrimRight(strings.TrimSpace(apiBaseURL), "/")
+	if err := validateHTTPAPIBaseURL(apiBaseURL); err != nil {
+		return nil, err
+	}
+	gatewayURL = strings.TrimSpace(gatewayURL)
+	if err := validateGatewayURL(gatewayURL); err != nil {
+		return nil, err
+	}
 	return &Client{
 		appID:        appID,
 		clientSecret: clientSecret,
-		apiBaseURL:   strings.TrimRight(apiBaseURL, "/"),
-		gatewayURL:   strings.TrimSpace(gatewayURL),
-		httpClient:   &http.Client{Timeout: 15 * time.Second},
+		apiBaseURL:   apiBaseURL,
+		gatewayURL:   gatewayURL,
+		httpClient: secutils.NewSSRFSafeHTTPClient(secutils.SSRFSafeHTTPClientConfig{
+			Timeout:      15 * time.Second,
+			MaxRedirects: 5,
+		}),
 	}, nil
 }
 
@@ -55,9 +69,48 @@ func (c *Client) GatewayURL(ctx context.Context) (string, error) {
 	if result.URL == "" {
 		return "", fmt.Errorf("empty qqbot gateway url")
 	}
+	if err := validateGatewayURL(result.URL); err != nil {
+		return "", fmt.Errorf("invalid qqbot gateway url: %w", err)
+	}
 	return result.URL, nil
 }
 
+func validateHTTPAPIBaseURL(raw string) error {
+	u, err := url.Parse(raw)
+	if err != nil || u.Host == "" {
+		return fmt.Errorf("invalid qqbot api_base_url: must be a valid http(s) URL")
+	}
+	if u.Scheme != "http" && u.Scheme != "https" {
+		return fmt.Errorf("invalid qqbot api_base_url: must use http or https")
+	}
+	if err := secutils.ValidateURLForSSRF(raw); err != nil {
+		return fmt.Errorf("invalid qqbot api_base_url: %w (for private deployments, add the hostname to SSRF_WHITELIST)", err)
+	}
+	return nil
+}
+
+func validateGatewayURL(raw string) error {
+	if strings.TrimSpace(raw) == "" {
+		return nil
+	}
+	u, err := url.Parse(raw)
+	if err != nil || u.Host == "" {
+		return fmt.Errorf("gateway_url must be a valid wss URL")
+	}
+	if u.Scheme != "wss" {
+		return fmt.Errorf("gateway_url must use wss")
+	}
+	checkURL := *u
+	checkURL.Scheme = "https"
+	if err := secutils.ValidateURLForSSRF(checkURL.String()); err != nil {
+		return fmt.Errorf(
+			"gateway_url failed SSRF validation: %w (for private deployments, add the hostname to SSRF_WHITELIST)",
+			err,
+		)
+	}
+	return nil
+}
+
 func (c *Client) SendC2CMessage(ctx context.Context, openID, content, msgID string) error {
 	path := fmt.Sprintf("/v2/users/%s/messages", openID)
 	return c.sendText(ctx, path, content, msgID)
diff --git a/internal/models/chat/ollama.go b/internal/models/chat/ollama.go
index 989a06fad..45f397d69 100644
--- a/internal/models/chat/ollama.go
+++ b/internal/models/chat/ollama.go
@@ -5,7 +5,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
-	"net/http"
 	"strconv"
 	"strings"
 	"time"
@@ -13,6 +12,7 @@ import (
 	"github.com/Tencent/WeKnora/internal/logger"
 	"github.com/Tencent/WeKnora/internal/models/utils/ollama"
 	"github.com/Tencent/WeKnora/internal/types"
+	secutils "github.com/Tencent/WeKnora/internal/utils"
 	ollamaapi "github.com/ollama/ollama/api"
 )
 
@@ -63,7 +63,13 @@ func resolveImageForOllama(imageURL string) ollamaapi.ImageData {
 		return data
 	}
 	if strings.HasPrefix(imageURL, "http://") || strings.HasPrefix(imageURL, "https://") {
-		client := &http.Client{Timeout: 30 * time.Second}
+		if err := secutils.ValidateURLForSSRF(imageURL); err != nil {
+			return nil
+		}
+		client := secutils.NewSSRFSafeHTTPClient(secutils.SSRFSafeHTTPClientConfig{
+			Timeout:      30 * time.Second,
+			MaxRedirects: 5,
+		})
 		resp, err := client.Get(imageURL)
 		if err != nil {
 			return nil
diff --git a/internal/models/chat/ollama_test.go b/internal/models/chat/ollama_test.go
new file mode 100644
index 000000000..837702699
--- /dev/null
+++ b/internal/models/chat/ollama_test.go
@@ -0,0 +1,34 @@
+package chat
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	secutils "github.com/Tencent/WeKnora/internal/utils"
+)
+
+func TestResolveImageForOllamaRejectsInternalURL(t *testing.T) {
+	t.Setenv("SSRF_WHITELIST", "")
+	secutils.ResetSSRFWhitelistForTest()
+	t.Cleanup(secutils.ResetSSRFWhitelistForTest)
+
+	if data := resolveImageForOllama("http://169.254.169.254/latest/meta-data/"); data != nil {
+		t.Fatalf("resolveImageForOllama returned data for blocked internal URL")
+	}
+}
+
+func TestResolveImageForOllamaBlocksRedirectToInternalURL(t *testing.T) {
+	t.Setenv("SSRF_WHITELIST", "127.0.0.1")
+	secutils.ResetSSRFWhitelistForTest()
+	t.Cleanup(secutils.ResetSSRFWhitelistForTest)
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		http.Redirect(w, r, "http://169.254.169.254/latest/meta-data/", http.StatusFound)
+	}))
+	defer server.Close()
+
+	if data := resolveImageForOllama(server.URL); data != nil {
+		t.Fatalf("resolveImageForOllama returned data after redirect to blocked internal URL")
+	}
+}
diff --git a/internal/router/router.go b/internal/router/router.go
index 095429462..ce7c8df0c 100644
--- a/internal/router/router.go
+++ b/internal/router/router.go
@@ -1465,28 +1465,12 @@ func newFileServeHandler(globalFileService interfaces.FileService) gin.HandlerFu
 		}
 		defer reader.Close()
 
-		ext := filepath.Ext(filePath)
-		contentType := "application/octet-stream"
-		switch strings.ToLower(ext) {
-		case ".png":
-			contentType = "image/png"
-		case ".jpg", ".jpeg":
-			contentType = "image/jpeg"
-		case ".gif":
-			contentType = "image/gif"
-		case ".webp":
-			contentType = "image/webp"
-		case ".bmp":
-			contentType = "image/bmp"
-		case ".svg":
-			contentType = "image/svg+xml"
-		case ".pdf":
-			contentType = "application/pdf"
-		case ".csv":
-			contentType = "text/csv; charset=utf-8"
-		}
-
+		contentType, inline := secutils.SafeContentTypeByFilename(filePath)
 		c.Header("Content-Type", contentType)
+		c.Header("X-Content-Type-Options", "nosniff")
+		if !inline {
+			c.Header("Content-Disposition", "attachment")
+		}
 		c.Header("Cache-Control", "public, max-age=86400")
 		c.Status(http.StatusOK)
 		if _, err := io.Copy(c.Writer, reader); err != nil {
@@ -1587,24 +1571,7 @@ func presignedFileHandler(tenantService interfaces.TenantService, absDir string)
 			return
 		}
 
-		ext := filepath.Ext(filePath)
-		contentType := "application/octet-stream"
-		switch strings.ToLower(ext) {
-		case ".png":
-			contentType = "image/png"
-		case ".jpg", ".jpeg":
-			contentType = "image/jpeg"
-		case ".gif":
-			contentType = "image/gif"
-		case ".webp":
-			contentType = "image/webp"
-		case ".bmp":
-			contentType = "image/bmp"
-		case ".svg":
-			contentType = "image/svg+xml"
-		case ".pdf":
-			contentType = "application/pdf"
-		}
+		contentType, inline := secutils.SafeContentTypeByFilename(filePath)
 
 		// HEAD short-circuits the body read. We still need to confirm the
 		// object exists, but we use a 0-byte content length and skip io.Copy.
@@ -1621,6 +1588,10 @@ func presignedFileHandler(tenantService interfaces.TenantService, absDir string)
 		defer reader.Close()
 
 		c.Header("Content-Type", contentType)
+		c.Header("X-Content-Type-Options", "nosniff")
+		if !inline {
+			c.Header("Content-Disposition", "attachment")
+		}
 		c.Header("Cache-Control", "public, max-age=86400")
 		if c.Request.Method == http.MethodHead {
 			c.Status(http.StatusOK)
diff --git a/internal/router/router_files_test.go b/internal/router/router_files_test.go
index 8923f5f2f..f0eec566a 100644
--- a/internal/router/router_files_test.go
+++ b/internal/router/router_files_test.go
@@ -152,3 +152,35 @@ func TestServeFilesRejectsPathWithoutTenantSegment(t *testing.T) {
 		t.Fatalf("status = %d, want %d", got, want)
 	}
 }
+
+func TestServeFilesForcesActiveContentDownload(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	t.Setenv("STORAGE_TYPE", "local")
+
+	engine := gin.New()
+	serveFiles(engine, &stubFileService{
+		getFile: func(_ context.Context, _ string) (io.ReadCloser, error) {
+			return io.NopCloser(strings.NewReader(`<svg onload="alert(1)"></svg>`)), nil
+		},
+	})
+
+	filePath := "local://42/docs/payload.svg"
+	req := httptest.NewRequest(http.MethodGet, "/files?file_path="+url.QueryEscape(filePath), nil)
+	req = req.WithContext(context.WithValue(req.Context(), types.TenantInfoContextKey, &types.Tenant{ID: 42}))
+
+	recorder := httptest.NewRecorder()
+	engine.ServeHTTP(recorder, req)
+
+	if got, want := recorder.Code, http.StatusOK; got != want {
+		t.Fatalf("status = %d, want %d", got, want)
+	}
+	if got := recorder.Header().Get("Content-Type"); got != "application/octet-stream" {
+		t.Fatalf("Content-Type = %q, want application/octet-stream", got)
+	}
+	if got := recorder.Header().Get("Content-Disposition"); got != "attachment" {
+		t.Fatalf("Content-Disposition = %q, want attachment", got)
+	}
+	if got := recorder.Header().Get("X-Content-Type-Options"); got != "nosniff" {
+		t.Fatalf("X-Content-Type-Options = %q, want nosniff", got)
+	}
+}
diff --git a/internal/router/router_presigned_test.go b/internal/router/router_presigned_test.go
index 186e2ea7a..6c4cc8573 100644
--- a/internal/router/router_presigned_test.go
+++ b/internal/router/router_presigned_test.go
@@ -170,6 +170,28 @@ func TestPresignedFile_GET_ReturnsContent(t *testing.T) {
 	}
 }
 
+func TestPresignedFile_ForcesActiveContentDownload(t *testing.T) {
+	engine, baseDir, signURL := setupPresignedTestServer(t)
+	storagePath := writeTestFile(t, baseDir, "1/payload.svg", `<svg onload="alert(1)"></svg>`)
+
+	req := httptest.NewRequest(http.MethodGet, signURL(storagePath, 1, time.Hour), nil)
+	w := httptest.NewRecorder()
+	engine.ServeHTTP(w, req)
+
+	if got, want := w.Code, http.StatusOK; got != want {
+		t.Fatalf("status = %d, want %d", got, want)
+	}
+	if got := w.Header().Get("Content-Type"); got != "application/octet-stream" {
+		t.Fatalf("Content-Type = %q, want application/octet-stream", got)
+	}
+	if got := w.Header().Get("Content-Disposition"); got != "attachment" {
+		t.Fatalf("Content-Disposition = %q, want attachment", got)
+	}
+	if got := w.Header().Get("X-Content-Type-Options"); got != "nosniff" {
+		t.Fatalf("X-Content-Type-Options = %q, want nosniff", got)
+	}
+}
+
 func TestPresignedFile_InvalidSig_403(t *testing.T) {
 	engine, _, _ := setupPresignedTestServer(t)
 
diff --git a/internal/utils/fileutil.go b/internal/utils/fileutil.go
index 341ddcc0d..6d53ee825 100644
--- a/internal/utils/fileutil.go
+++ b/internal/utils/fileutil.go
@@ -2,8 +2,24 @@ package utils
 
 import "strings"
 
+// IsActiveBrowserContentExt reports whether a file extension can execute script
+// or otherwise participate as active same-origin browser content when served
+// inline. User-uploaded files with these extensions must be downloaded instead
+// of previewed inline.
+func IsActiveBrowserContentExt(ext string) bool {
+	switch strings.ToLower(ext) {
+	case ".svg", ".svgz", ".html", ".htm", ".xhtml", ".xml", ".js", ".mjs", ".css":
+		return true
+	default:
+		return false
+	}
+}
+
 // GetContentTypeByExt returns the content type based on file extension
 func GetContentTypeByExt(ext string) string {
+	if IsActiveBrowserContentExt(ext) {
+		return "application/octet-stream"
+	}
 	switch strings.ToLower(ext) {
 	case ".csv":
 		return "text/csv; charset=utf-8"
@@ -27,12 +43,8 @@ func GetContentTypeByExt(ext string) string {
 		return "image/gif"
 	case ".webp":
 		return "image/webp"
-	case ".svg":
-		return "image/svg+xml"
 	case ".txt":
 		return "text/plain; charset=utf-8"
-	case ".html", ".htm":
-		return "text/html; charset=utf-8"
 	case ".mp4":
 		return "video/mp4"
 	case ".mp3":
@@ -51,3 +63,18 @@ func GetContentTypeByExt(ext string) string {
 		return "application/octet-stream"
 	}
 }
+
+// SafeContentTypeByFilename returns a browser-safe content type for serving
+// user-controlled files and whether that file may be displayed inline.
+func SafeContentTypeByFilename(filename string) (string, bool) {
+	ext := filename
+	if idx := strings.LastIndex(ext, "."); idx >= 0 {
+		ext = ext[idx:]
+	} else {
+		ext = ""
+	}
+	if IsActiveBrowserContentExt(ext) {
+		return "application/octet-stream", false
+	}
+	return GetContentTypeByExt(ext), true
+}