diff --git a/internal/handler/download_client_handler.go b/internal/handler/download_client_handler.go
index c7b11b6..a2d7c7b 100644
--- a/internal/handler/download_client_handler.go
+++ b/internal/handler/download_client_handler.go
@@ -57,6 +57,11 @@ func (h *DownloadClientHandler) Create(c *gin.Context) {
 
 	ctx := c.Request.Context()
 	_ = h.svc.Repo.Setting.Set(ctx, "download_clients.managed", "true")
+	normalizedHost, err := service.NormalizeDownloadClientHost(req.Type, req.Host)
+	if err != nil {
+		Error(c, http.StatusBadRequest, ErrInvalidParams, err.Error())
+		return
+	}
 
 	// 加密密码
 	password := req.Password
@@ -82,7 +87,7 @@ func (h *DownloadClientHandler) Create(c *gin.Context) {
 	client := &model.DownloadClient{
 		Name:      req.Name,
 		Type:      req.Type,
-		Host:      req.Host,
+		Host:      normalizedHost,
 		Username:  req.Username,
 		Password:  password,
 		IsDefault: req.IsDefault,
@@ -152,7 +157,16 @@ func (h *DownloadClientHandler) Update(c *gin.Context) {
 		client.Type = req.Type
 	}
 	if req.Host != "" {
-		client.Host = req.Host
+		clientType := client.Type
+		if req.Type != "" {
+			clientType = req.Type
+		}
+		normalizedHost, err := service.NormalizeDownloadClientHost(clientType, req.Host)
+		if err != nil {
+			Error(c, http.StatusBadRequest, ErrInvalidParams, err.Error())
+			return
+		}
+		client.Host = normalizedHost
 	}
 	if req.Username != "" {
 		client.Username = req.Username
@@ -180,6 +194,12 @@ func (h *DownloadClientHandler) Update(c *gin.Context) {
 			client.Extra = extraStr
 		}
 	}
+	normalizedHost, err := service.NormalizeDownloadClientHost(client.Type, client.Host)
+	if err != nil {
+		Error(c, http.StatusBadRequest, ErrInvalidParams, err.Error())
+		return
+	}
+	client.Host = normalizedHost
 
 	if err := h.svc.Repo.DownloadClient.Update(ctx, client); err != nil {
 		Error(c, http.StatusInternalServerError, ErrInternal, "更新失败")
diff --git a/internal/service/aria2_adp.go b/internal/service/aria2_adp.go
index 15708bf..71b6fb7 100644
--- a/internal/service/aria2_adp.go
+++ b/internal/service/aria2_adp.go
@@ -57,6 +57,11 @@ func NewAria2Adapter() *Aria2Adapter {
 func (a *Aria2Adapter) Initialize(ctx context.Context, cfg DownloadClientConfig) error {
 	a.mu.Lock()
 	defer a.mu.Unlock()
+	endpoint, err := normalizeDownloadClientEndpoint("aria2", cfg.Host)
+	if err != nil {
+		return err
+	}
+	cfg.Host = endpoint
 	a.cfg = cfg
 	a.idSeq = 0
 	return a.getVersionLocked(ctx)
@@ -71,9 +76,9 @@ func (a *Aria2Adapter) Ping(ctx context.Context) error {
 
 // getVersionLocked 内部版本检查（调用者必须持有锁）。
 func (a *Aria2Adapter) getVersionLocked(ctx context.Context) error {
-	rpcURL := a.cfg.Host
-	if !strings.HasSuffix(rpcURL, "/jsonrpc") {
-		rpcURL = strings.TrimRight(rpcURL, "/") + "/jsonrpc"
+	rpcURL, err := downloadClientRPCURL("aria2", a.cfg.Host)
+	if err != nil {
+		return err
 	}
 
 	req := &aria2Request{
@@ -88,7 +93,7 @@ func (a *Aria2Adapter) getVersionLocked(ctx context.Context) error {
 		return err
 	}
 
-	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, rpcURL, bytes.NewReader(body))
+	httpReq, err := newDownloadClientHTTPRequest(ctx, http.MethodPost, rpcURL, bytes.NewReader(body))
 	if err != nil {
 		return err
 	}
@@ -110,9 +115,9 @@ func (a *Aria2Adapter) getVersionLocked(ctx context.Context) error {
 
 // rpcLocked 发送 JSON-RPC 请求（调用者必须持有锁）。
 func (a *Aria2Adapter) rpcLocked(ctx context.Context, method string, params []interface{}) (json.RawMessage, error) {
-	rpcURL := a.cfg.Host
-	if !strings.HasSuffix(rpcURL, "/jsonrpc") {
-		rpcURL = strings.TrimRight(rpcURL, "/") + "/jsonrpc"
+	rpcURL, err := downloadClientRPCURL("aria2", a.cfg.Host)
+	if err != nil {
+		return nil, err
 	}
 
 	if params == nil {
@@ -145,7 +150,7 @@ func (a *Aria2Adapter) rpcLocked(ctx context.Context, method string, params []in
 		return nil, err
 	}
 
-	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, rpcURL, bytes.NewReader(body))
+	httpReq, err := newDownloadClientHTTPRequest(ctx, http.MethodPost, rpcURL, bytes.NewReader(body))
 	if err != nil {
 		return nil, err
 	}
diff --git a/internal/service/download_client_endpoint.go b/internal/service/download_client_endpoint.go
new file mode 100644
index 0000000..58a3e0c
--- /dev/null
+++ b/internal/service/download_client_endpoint.go
@@ -0,0 +1,115 @@
+package service
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+var downloadClientEndpointPattern = regexp.MustCompile(`^https?://(?:[A-Za-z0-9.-]+|\[[0-9A-Fa-f:.]+\])(?::[0-9]{1,5})?(?:/[A-Za-z0-9._~%!$&'()*+,;=:@/-]*)?$`)
+
+func NormalizeDownloadClientHost(clientType, raw string) (string, error) {
+	return normalizeDownloadClientEndpoint(clientType, raw)
+}
+
+func normalizeDownloadClientEndpoint(clientType, raw string) (string, error) {
+	raw = strings.TrimSpace(raw)
+	if raw == "" {
+		return "", errors.New("host required")
+	}
+	if strings.ContainsAny(raw, "\r\n\t") {
+		return "", errors.New("host contains invalid control characters")
+	}
+	if !strings.Contains(raw, "://") {
+		raw = "http://" + raw
+	}
+	if !downloadClientEndpointPattern.MatchString(raw) {
+		return "", errors.New("host must be a valid http(s) URL without username, query, or fragment")
+	}
+	parsed, err := url.Parse(raw)
+	if err != nil || parsed.Scheme == "" || parsed.Host == "" {
+		return "", errors.New("host must be a valid http(s) URL")
+	}
+	scheme := strings.ToLower(parsed.Scheme)
+	if scheme != "http" && scheme != "https" {
+		return "", errors.New("host only supports http or https")
+	}
+	if parsed.User != nil || parsed.RawQuery != "" || parsed.Fragment != "" {
+		return "", errors.New("host must not include username, query, or fragment")
+	}
+	if strings.TrimSpace(parsed.Hostname()) == "" {
+		return "", errors.New("host must include a hostname")
+	}
+	if port := parsed.Port(); port != "" {
+		n, err := strconv.Atoi(port)
+		if err != nil || n < 1 || n > 65535 {
+			return "", errors.New("host port must be between 1 and 65535")
+		}
+	}
+	if err := validateDownloadClientPath(clientType, parsed.Path); err != nil {
+		return "", err
+	}
+	parsed.Scheme = scheme
+	parsed.Path = strings.TrimRight(parsed.Path, "/")
+	parsed.RawPath = ""
+	parsed.RawQuery = ""
+	parsed.Fragment = ""
+	return strings.TrimRight(parsed.String(), "/"), nil
+}
+
+func validateDownloadClientPath(clientType, rawPath string) error {
+	rawPath = strings.TrimSpace(rawPath)
+	if rawPath == "" || rawPath == "/" {
+		return nil
+	}
+	for _, segment := range strings.Split(rawPath, "/") {
+		if segment == "." || segment == ".." {
+			return errors.New("host path must not contain traversal segments")
+		}
+	}
+	switch clientType {
+	case "qbittorrent", "aria2", "transmission":
+		return nil
+	default:
+		return fmt.Errorf("unsupported client type %q", clientType)
+	}
+}
+
+func downloadClientRPCURL(clientType, host string) (string, error) {
+	base, err := normalizeDownloadClientEndpoint(clientType, host)
+	if err != nil {
+		return "", err
+	}
+	u, err := url.Parse(base)
+	if err != nil {
+		return "", err
+	}
+	switch clientType {
+	case "aria2":
+		if !strings.HasSuffix(strings.ToLower(u.Path), "/jsonrpc") {
+			u.Path = strings.TrimRight(u.Path, "/") + "/jsonrpc"
+		}
+	case "transmission":
+		if !strings.Contains(strings.ToLower(u.Path), "/rpc") {
+			u.Path = strings.TrimRight(u.Path, "/") + "/transmission/rpc"
+		}
+	case "qbittorrent":
+	default:
+		return "", fmt.Errorf("unsupported client type %q", clientType)
+	}
+	return u.String(), nil
+}
+
+func newDownloadClientHTTPRequest(ctx context.Context, method, endpoint string, body io.Reader) (*http.Request, error) {
+	endpoint = strings.TrimSpace(endpoint)
+	if !downloadClientEndpointPattern.MatchString(endpoint) {
+		return nil, errors.New("download client endpoint failed safety validation")
+	}
+	return http.NewRequestWithContext(ctx, method, endpoint, body)
+}
diff --git a/internal/service/download_clients.go b/internal/service/download_clients.go
index 2971bb9..0d342bd 100644
--- a/internal/service/download_clients.go
+++ b/internal/service/download_clients.go
@@ -9,7 +9,6 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
-	"net/url"
 	"strings"
 	"time"
 
@@ -150,7 +149,14 @@ func (s *DownloadClientService) Test(ctx context.Context, id string) error {
 	case "qbittorrent":
 		return qbitLogin(ctx, s.client, c.Host, c.Username, c.Password)
 	case "aria2", "transmission":
-		req, _ := http.NewRequestWithContext(ctx, http.MethodGet, c.Host, nil)
+		endpoint, err := downloadClientRPCURL(c.Type, c.Host)
+		if err != nil {
+			return err
+		}
+		req, err := newDownloadClientHTTPRequest(ctx, http.MethodGet, endpoint, nil)
+		if err != nil {
+			return err
+		}
 		resp, err := s.client.Do(req)
 		if err != nil {
 			return err
@@ -175,12 +181,19 @@ func (s *DownloadClientService) Aria2GlobalStats(ctx context.Context, clientID s
 	if c == nil || c.Type != "aria2" {
 		return nil, errors.New("aria2 client not found")
 	}
+	endpoint, err := downloadClientRPCURL("aria2", c.Host)
+	if err != nil {
+		return nil, err
+	}
 	payload := fmt.Sprintf(
 		`{"jsonrpc":"2.0","id":"x","method":"aria2.getGlobalStat","params":["token:%s"]}`,
 		c.Password,
 	)
-	req, _ := http.NewRequestWithContext(ctx, http.MethodPost, c.Host,
+	req, err := newDownloadClientHTTPRequest(ctx, http.MethodPost, endpoint,
 		strings.NewReader(payload))
+	if err != nil {
+		return nil, err
+	}
 	req.Header.Set("Content-Type", "application/json")
 	resp, err := s.client.Do(req)
 	if err != nil {
@@ -221,14 +234,11 @@ func normalizeDownloadClientInput(in DownloadClientInput) (DownloadClientInput,
 	if !strings.Contains(in.Host, "://") {
 		in.Host = "http://" + in.Host
 	}
-	parsed, err := url.Parse(in.Host)
-	if err != nil || parsed.Host == "" {
-		return in, errors.New("host must be a valid http(s) URL")
+	normalized, err := normalizeDownloadClientEndpoint(in.Type, in.Host)
+	if err != nil {
+		return in, err
 	}
-	if parsed.Scheme != "http" && parsed.Scheme != "https" {
-		return in, errors.New("host only supports http or https")
-	}
-	in.Host = strings.TrimRight(parsed.String(), "/")
+	in.Host = normalized
 	return in, nil
 }
 
diff --git a/internal/service/download_clients_test.go b/internal/service/download_clients_test.go
index 6c720f0..6db5d1c 100644
--- a/internal/service/download_clients_test.go
+++ b/internal/service/download_clients_test.go
@@ -1,6 +1,8 @@
 package service
 
 import (
+	"net/http"
+	"net/http/httptest"
 	"testing"
 
 	"github.com/glebarez/sqlite"
@@ -81,6 +83,95 @@ func TestDownloadClientRejectsUnsupportedHostScheme(t *testing.T) {
 	}
 }
 
+func TestDownloadClientRejectsUnsafeEndpointParts(t *testing.T) {
+	db, err := gorm.Open(sqlite.Open(":memory:"), &gorm.Config{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := db.AutoMigrate(&model.DownloadClient{}, &model.Setting{}); err != nil {
+		t.Fatal(err)
+	}
+	svc := NewDownloadClientService(zap.NewNop(), repository.New(db))
+
+	for _, host := range []string{
+		"http://user:pass@127.0.0.1:6800",
+		"http://127.0.0.1:6800/jsonrpc?target=http://169.254.169.254",
+		"http://127.0.0.1:6800/jsonrpc#fragment",
+		"http://127.0.0.1:70000",
+		"file:///etc/passwd",
+	} {
+		if _, err := svc.Create(t.Context(), DownloadClientInput{
+			Name:    "bad",
+			Type:    "aria2",
+			Host:    host,
+			Enabled: true,
+		}); err == nil {
+			t.Fatalf("Create allowed unsafe host %q", host)
+		}
+	}
+}
+
+func TestDownloadClientRPCURLAppendsExpectedPath(t *testing.T) {
+	cases := []struct {
+		clientType string
+		host       string
+		want       string
+	}{
+		{"aria2", "127.0.0.1:6800", "http://127.0.0.1:6800/jsonrpc"},
+		{"aria2", "http://nas.local:6800/rpc", "http://nas.local:6800/rpc/jsonrpc"},
+		{"transmission", "http://nas.local:9091", "http://nas.local:9091/transmission/rpc"},
+		{"transmission", "http://nas.local:9091/transmission/rpc", "http://nas.local:9091/transmission/rpc"},
+	}
+	for _, tc := range cases {
+		got, err := downloadClientRPCURL(tc.clientType, tc.host)
+		if err != nil {
+			t.Fatalf("downloadClientRPCURL(%q, %q) error: %v", tc.clientType, tc.host, err)
+		}
+		if got != tc.want {
+			t.Fatalf("downloadClientRPCURL(%q, %q) = %q, want %q", tc.clientType, tc.host, got, tc.want)
+		}
+	}
+}
+
+func TestAria2AdapterRejectsUnsafeHostBeforeHTTPRequest(t *testing.T) {
+	adapter := NewAria2Adapter()
+	called := false
+	adapter.client = &http.Client{Transport: roundTripFunc(func(*http.Request) (*http.Response, error) {
+		called = true
+		return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}, nil
+	})}
+
+	if err := adapter.Initialize(t.Context(), DownloadClientConfig{
+		Host:     "http://user:pass@127.0.0.1:6800",
+		Password: "secret",
+	}); err == nil {
+		t.Fatal("expected unsafe host error")
+	}
+	if called {
+		t.Fatal("unsafe aria2 host should be rejected before any HTTP request")
+	}
+}
+
+func TestAria2AdapterUsesNormalizedRPCURL(t *testing.T) {
+	var gotPath string
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotPath = r.URL.Path
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer server.Close()
+
+	adapter := NewAria2Adapter()
+	if err := adapter.Initialize(t.Context(), DownloadClientConfig{
+		Host:     server.URL,
+		Password: "secret",
+	}); err != nil {
+		t.Fatal(err)
+	}
+	if gotPath != "/jsonrpc" {
+		t.Fatalf("aria2 request path = %q, want /jsonrpc", gotPath)
+	}
+}
+
 func TestDownloadClientDeleteClearsLegacyQBitConnectionWhenNoDefault(t *testing.T) {
 	db, err := gorm.Open(sqlite.Open(":memory:"), &gorm.Config{})
 	if err != nil {
diff --git a/internal/service/download_manager_svc.go b/internal/service/download_manager_svc.go
index 4cb9511..8c86812 100644
--- a/internal/service/download_manager_svc.go
+++ b/internal/service/download_manager_svc.go
@@ -22,9 +22,9 @@ type DownloadManager struct {
 	repo   *repository.Container
 	crypto *CryptoService
 
-	mu       sync.RWMutex
-	clients  map[string]DownloadAdapter // clientID -> adapter
-	configs  map[string]DownloadClientConfig
+	mu      sync.RWMutex
+	clients map[string]DownloadAdapter // clientID -> adapter
+	configs map[string]DownloadClientConfig
 }
 
 // NewDownloadManager 创建新的下载管理器。
@@ -230,9 +230,13 @@ func (m *DownloadManager) buildConfig(dc *model.DownloadClient) (DownloadClientC
 	if m.crypto != nil && password != "" {
 		password = m.crypto.Decrypt(password)
 	}
+	host, err := normalizeDownloadClientEndpoint(dc.Type, dc.Host)
+	if err != nil {
+		return DownloadClientConfig{}, err
+	}
 
 	cfg := DownloadClientConfig{
-		Host:     dc.Host,
+		Host:     host,
 		Username: dc.Username,
 		Password: password,
 	}
diff --git a/internal/service/qbittorrent.go b/internal/service/qbittorrent.go
index e38b5e4..ce2e8c3 100644
--- a/internal/service/qbittorrent.go
+++ b/internal/service/qbittorrent.go
@@ -78,7 +78,7 @@ var (
 // an unconfigured downloader must fail closed instead of silently trying a
 // localhost qBittorrent instance.
 func NewQBitClient(log *zap.Logger, cfg QBitConfig) *QBitClient {
-	cfg.BaseURL = strings.TrimRight(strings.TrimSpace(cfg.BaseURL), "/")
+	cfg.BaseURL = normalizeQBitBaseURL(cfg.BaseURL)
 	jar, _ := cookiejar.New(nil)
 	client := NewInternalHTTPClient(20 * time.Second)
 	client.Jar = jar
@@ -93,7 +93,7 @@ func NewQBitClient(log *zap.Logger, cfg QBitConfig) *QBitClient {
 func (q *QBitClient) Configure(cfg QBitConfig) {
 	q.mu.Lock()
 	defer q.mu.Unlock()
-	cfg.BaseURL = strings.TrimRight(strings.TrimSpace(cfg.BaseURL), "/")
+	cfg.BaseURL = normalizeQBitBaseURL(cfg.BaseURL)
 	q.cfg = cfg
 	jar, _ := cookiejar.New(nil)
 	q.client.Jar = jar
@@ -105,6 +105,18 @@ func (q *QBitClient) IsConfigured() bool {
 	return strings.TrimSpace(q.cfg.BaseURL) != ""
 }
 
+func normalizeQBitBaseURL(raw string) string {
+	raw = strings.TrimSpace(raw)
+	if raw == "" {
+		return ""
+	}
+	normalized, err := normalizeDownloadClientEndpoint("qbittorrent", raw)
+	if err != nil {
+		return strings.TrimRight(raw, "/")
+	}
+	return normalized
+}
+
 // Login performs POST /api/v2/auth/login.
 func (q *QBitClient) Login(ctx context.Context) error {
 	if q.cfg.BaseURL == "" {
@@ -193,9 +205,8 @@ func (q *QBitClient) addTorrentLocked(ctx context.Context, magnetOrURL string, t
 	}
 	_ = w.Close()
 
-	req, err := http.NewRequestWithContext(ctx, http.MethodPost,
-		strings.TrimRight(q.cfg.BaseURL, "/")+"/api/v2/torrents/add", body,
-	)
+	req, err := newDownloadClientHTTPRequest(ctx, http.MethodPost,
+		strings.TrimRight(q.cfg.BaseURL, "/")+"/api/v2/torrents/add", body)
 	if err != nil {
 		return err
 	}
@@ -427,13 +438,15 @@ func (q *QBitClient) List(ctx context.Context, filter string) ([]QBitTorrent, er
 
 func (q *QBitClient) listLocked(ctx context.Context, filter string) ([]QBitTorrent, error) {
 	u := strings.TrimRight(q.cfg.BaseURL, "/") + "/api/v2/torrents/info"
-	if filter != "" {
-		u += "?filter=" + url.QueryEscape(filter)
-	}
-	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u, nil)
+	req, err := newDownloadClientHTTPRequest(ctx, http.MethodGet, u, nil)
 	if err != nil {
 		return nil, err
 	}
+	if filter != "" {
+		query := req.URL.Query()
+		query.Set("filter", filter)
+		req.URL.RawQuery = query.Encode()
+	}
 	req.Header.Set("Referer", q.cfg.BaseURL)
 	resp, err := q.client.Do(req)
 	if err != nil {
@@ -464,10 +477,9 @@ func (q *QBitClient) Delete(ctx context.Context, hash string, deleteFiles bool)
 	} else {
 		form.Set("deleteFiles", "false")
 	}
-	req, err := http.NewRequestWithContext(ctx, http.MethodPost,
+	req, err := newDownloadClientHTTPRequest(ctx, http.MethodPost,
 		strings.TrimRight(q.cfg.BaseURL, "/")+"/api/v2/torrents/delete",
-		strings.NewReader(form.Encode()),
-	)
+		strings.NewReader(form.Encode()))
 	if err != nil {
 		return err
 	}
@@ -504,10 +516,9 @@ func (q *QBitClient) SetLocation(ctx context.Context, hash, location string) err
 	form := url.Values{}
 	form.Set("hashes", hash)
 	form.Set("location", location)
-	req, err := http.NewRequestWithContext(ctx, http.MethodPost,
+	req, err := newDownloadClientHTTPRequest(ctx, http.MethodPost,
 		strings.TrimRight(q.cfg.BaseURL, "/")+"/api/v2/torrents/setLocation",
-		strings.NewReader(form.Encode()),
-	)
+		strings.NewReader(form.Encode()))
 	if err != nil {
 		return err
 	}
diff --git a/internal/service/qbittorrent_adp.go b/internal/service/qbittorrent_adp.go
index e108c33..779e2d2 100644
--- a/internal/service/qbittorrent_adp.go
+++ b/internal/service/qbittorrent_adp.go
@@ -42,6 +42,11 @@ func NewQBitAdapter() *QBitAdapter {
 func (a *QBitAdapter) Initialize(ctx context.Context, cfg DownloadClientConfig) error {
 	a.mu.Lock()
 	defer a.mu.Unlock()
+	endpoint, err := normalizeDownloadClientEndpoint("qbittorrent", cfg.Host)
+	if err != nil {
+		return err
+	}
+	cfg.Host = endpoint
 	a.cfg = cfg
 	a.LoggedIn = false
 	jar, _ := cookiejar.New(nil)
@@ -73,7 +78,7 @@ func (a *QBitAdapter) AddTorrent(ctx context.Context, torrentURL, savePath strin
 	_ = w.Close()
 
 	baseURL := strings.TrimRight(a.cfg.Host, "/")
-	req, err := http.NewRequestWithContext(ctx, http.MethodPost,
+	req, err := newDownloadClientHTTPRequest(ctx, http.MethodPost,
 		baseURL+"/api/v2/torrents/add", body)
 	if err != nil {
 		return "", err
@@ -108,7 +113,7 @@ func (a *QBitAdapter) Pause(ctx context.Context, hash string) error {
 	baseURL := strings.TrimRight(a.cfg.Host, "/")
 	form := url.Values{}
 	form.Set("hashes", hash)
-	req, err := http.NewRequestWithContext(ctx, http.MethodPost,
+	req, err := newDownloadClientHTTPRequest(ctx, http.MethodPost,
 		baseURL+"/api/v2/torrents/pause", strings.NewReader(form.Encode()))
 	if err != nil {
 		return err
@@ -136,7 +141,7 @@ func (a *QBitAdapter) Resume(ctx context.Context, hash string) error {
 	baseURL := strings.TrimRight(a.cfg.Host, "/")
 	form := url.Values{}
 	form.Set("hashes", hash)
-	req, err := http.NewRequestWithContext(ctx, http.MethodPost,
+	req, err := newDownloadClientHTTPRequest(ctx, http.MethodPost,
 		baseURL+"/api/v2/torrents/resume", strings.NewReader(form.Encode()))
 	if err != nil {
 		return err
@@ -169,7 +174,7 @@ func (a *QBitAdapter) Remove(ctx context.Context, hash string, deleteFiles bool)
 	} else {
 		form.Set("deleteFiles", "false")
 	}
-	req, err := http.NewRequestWithContext(ctx, http.MethodPost,
+	req, err := newDownloadClientHTTPRequest(ctx, http.MethodPost,
 		baseURL+"/api/v2/torrents/delete", strings.NewReader(form.Encode()))
 	if err != nil {
 		return err
@@ -196,13 +201,15 @@ func (a *QBitAdapter) List(ctx context.Context, filter string) ([]TorrentInfo, e
 	}
 	baseURL := strings.TrimRight(a.cfg.Host, "/")
 	u := baseURL + "/api/v2/torrents/info"
-	if filter != "" {
-		u += "?filter=" + url.QueryEscape(filter)
-	}
-	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u, nil)
+	req, err := newDownloadClientHTTPRequest(ctx, http.MethodGet, u, nil)
 	if err != nil {
 		return nil, err
 	}
+	if filter != "" {
+		query := req.URL.Query()
+		query.Set("filter", filter)
+		req.URL.RawQuery = query.Encode()
+	}
 	req.Header.Set("Referer", baseURL)
 	resp, err := a.client.Do(req)
 	if err != nil {
diff --git a/internal/service/qbittorrent_login.go b/internal/service/qbittorrent_login.go
index 8269dcc..f02d3fc 100644
--- a/internal/service/qbittorrent_login.go
+++ b/internal/service/qbittorrent_login.go
@@ -18,10 +18,15 @@ type qbitLoginVariant struct {
 }
 
 func qbitLogin(ctx context.Context, client *http.Client, baseURL, username, password string) error {
-	baseURL = strings.TrimRight(strings.TrimSpace(baseURL), "/")
+	baseURL = strings.TrimSpace(baseURL)
 	if baseURL == "" {
 		return errors.New("qbittorrent host not configured")
 	}
+	var err error
+	baseURL, err = normalizeDownloadClientEndpoint("qbittorrent", baseURL)
+	if err != nil {
+		return err
+	}
 	var lastErr error
 	for _, variant := range []qbitLoginVariant{
 		{name: "minimal"},
@@ -46,7 +51,7 @@ func qbitLoginOnce(ctx context.Context, client *http.Client, baseURL, username,
 	form := url.Values{}
 	form.Set("username", username)
 	form.Set("password", password)
-	req, err := http.NewRequestWithContext(ctx, http.MethodPost,
+	req, err := newDownloadClientHTTPRequest(ctx, http.MethodPost,
 		baseURL+"/api/v2/auth/login", strings.NewReader(form.Encode()))
 	if err != nil {
 		return err
diff --git a/internal/service/transmission_adp.go b/internal/service/transmission_adp.go
index 7d8434f..e6023dc 100644
--- a/internal/service/transmission_adp.go
+++ b/internal/service/transmission_adp.go
@@ -51,6 +51,11 @@ func NewTransmissionAdapter() *TransmissionAdapter {
 func (a *TransmissionAdapter) Initialize(ctx context.Context, cfg DownloadClientConfig) error {
 	a.mu.Lock()
 	defer a.mu.Unlock()
+	endpoint, err := normalizeDownloadClientEndpoint("transmission", cfg.Host)
+	if err != nil {
+		return err
+	}
+	cfg.Host = endpoint
 	a.cfg = cfg
 	a.sessionID = ""
 	a.tag = 0
@@ -66,13 +71,11 @@ func (a *TransmissionAdapter) Ping(ctx context.Context) error {
 
 // pingLocked 内部 ping 实现（调用者必须持有锁）。
 func (a *TransmissionAdapter) pingLocked(ctx context.Context) error {
-	rpcURL := a.cfg.Host
-	if !strings.HasSuffix(rpcURL, "/rpc") && !strings.HasSuffix(rpcURL, "/transmission/rpc") {
-		if !strings.Contains(rpcURL, "/rpc") {
-			rpcURL = strings.TrimRight(rpcURL, "/") + "/transmission/rpc"
-		}
+	rpcURL, err := downloadClientRPCURL("transmission", a.cfg.Host)
+	if err != nil {
+		return err
 	}
-	req, err := http.NewRequestWithContext(ctx, http.MethodGet, rpcURL, nil)
+	req, err := newDownloadClientHTTPRequest(ctx, http.MethodGet, rpcURL, nil)
 	if err != nil {
 		return err
 	}
@@ -98,9 +101,9 @@ func (a *TransmissionAdapter) pingLocked(ctx context.Context) error {
 
 // rpcLocked 发送 RPC 请求（调用者必须持有锁）。
 func (a *TransmissionAdapter) rpcLocked(ctx context.Context, method string, args map[string]interface{}) (*transmissionRPCResponse, error) {
-	rpcURL := a.cfg.Host
-	if !strings.Contains(rpcURL, "/rpc") {
-		rpcURL = strings.TrimRight(rpcURL, "/") + "/transmission/rpc"
+	rpcURL, err := downloadClientRPCURL("transmission", a.cfg.Host)
+	if err != nil {
+		return nil, err
 	}
 
 	a.tag++
@@ -114,7 +117,7 @@ func (a *TransmissionAdapter) rpcLocked(ctx context.Context, method string, args
 	}
 
 	for attempt := 0; attempt < 2; attempt++ {
-		req, err := http.NewRequestWithContext(ctx, http.MethodPost, rpcURL, bytes.NewReader(body))
+		req, err := newDownloadClientHTTPRequest(ctx, http.MethodPost, rpcURL, bytes.NewReader(body))
 		if err != nil {
 			return nil, err
 		}