fix(security): harden HTTP redirects by trust boundary

CMakeLists.txt

@@ -2226,3 +2226,10 @@ if(EXISTS "${_VLLM_CDNA_TEST_SRC}")
     target_link_libraries(test_vllm_cdna_gating PRIVATE lemonade-server-core)
     add_test(NAME VllmCdnaGatingTest COMMAND test_vllm_cdna_gating)
 endif()
+
+set(_HTTP_CLIENT_SECURITY_TEST_SRC "${CMAKE_CURRENT_SOURCE_DIR}/test/cpp/test_http_client_security.cpp")
+if(EXISTS "${_HTTP_CLIENT_SECURITY_TEST_SRC}")
+    add_executable(test_http_client_security test/cpp/test_http_client_security.cpp)
+    target_link_libraries(test_http_client_security PRIVATE lemonade-server-core)
+    add_test(NAME HttpClientSecurityTest COMMAND test_http_client_security)
+endif()

src/cpp/include/lemon/backends/cloud/cloud_server.h

@@ -83,7 +83,8 @@ class CloudServer : public WrappedServer {
     /// can continue with other providers.
     static std::vector<ModelInfo> discover_models(const std::string& provider,
                                                    const std::string& api_key,
-                                                   const std::string& base_url);
+                                                   const std::string& base_url,
+                                                   bool allow_insecure_http = false);
 
 private:
     struct ResolvedCreds {

src/cpp/include/lemon/utils/http_client.h

@@ -51,6 +51,23 @@ struct DownloadResult {
 using ProgressCallback = std::function<bool(size_t downloaded, size_t total)>;
 using StreamCallback = std::function<bool(const char* data, size_t length)>;
 
+// Trust boundary for HTTP requests that may follow redirects. Selects which URL
+// schemes are allowed for the initial request and for redirect targets, and
+// whether redirects are followed at all.
+enum class HttpSecurityPolicy {
+    // External hosts (Hugging Face, GitHub, release CDNs). Require https for the
+    // initial request and every redirect hop; bound the redirect chain. This is
+    // the default so untrusted destinations are HTTPS-only unless a caller opts
+    // out for a specific trust boundary.
+    ExternalHttpsOnly,
+    // Lemonade-managed backends reached over loopback http://127.0.0.1. Require
+    // http and never follow redirects.
+    TrustedLoopback,
+    // User-configured plaintext endpoints that explicitly opted in via
+    // allow_insecure_http. Permit http and https; bound the redirect chain.
+    AllowInsecureHttp,
+};
+
 // Download configuration options
 struct DownloadOptions {
     int max_retries = 5;              // Maximum retry attempts
@@ -86,7 +103,8 @@ class HttpClient {
     // Simple GET request. timeout_seconds=0 (default) uses default_timeout_seconds_.
     static HttpResponse get(const std::string& url,
                            const std::map<std::string, std::string>& headers = {},
-                           long timeout_seconds = 0);
+                           long timeout_seconds = 0,
+                           HttpSecurityPolicy policy = HttpSecurityPolicy::ExternalHttpsOnly);
 
     // Simple POST request
     static HttpResponse post(const std::string& url,
@@ -114,7 +132,8 @@ class HttpClient {
                                         const std::string& output_path,
                                         ProgressCallback callback = nullptr,
                                         const std::map<std::string, std::string>& headers = {},
-                                        const DownloadOptions& options = DownloadOptions());
+                                        const DownloadOptions& options = DownloadOptions(),
+                                        HttpSecurityPolicy policy = HttpSecurityPolicy::ExternalHttpsOnly);
 
     // Check if URL is reachable
     static bool is_reachable(const std::string& url, int timeout_seconds = 5);
@@ -129,7 +148,8 @@ class HttpClient {
                                            ProgressCallback callback,
                                            const std::map<std::string, std::string>& headers,
                                            const DownloadOptions& options,
-                                           bool initial_range_request);
+                                           bool initial_range_request,
+                                           HttpSecurityPolicy policy);
 };
 
 // Creates a throttled progress callback that prints at most once per second.

src/cpp/server/backends/acestep/acestep_server.cpp

@@ -205,7 +205,8 @@ bool AceStepServer::run_job(const std::string& path, const std::string& body,
     const std::string job_url = base + "/job?id=" + job_id;
     std::string status;
     for (int i = 0; i < 1200; ++i) {
-        auto poll = utils::HttpClient::get(job_url, {}, 30);
+        auto poll = utils::HttpClient::get(job_url, {}, 30,
+                                           utils::HttpSecurityPolicy::TrustedLoopback);
         if (poll.status_code == 200) {
             try { status = json::parse(poll.body).value("status", std::string()); }
             catch (...) { status.clear(); }
@@ -220,7 +221,8 @@ bool AceStepServer::run_job(const std::string& path, const std::string& body,
         return false;
     }
 
-    auto fetched = utils::HttpClient::get(job_url + "&result=1", {}, 120);
+    auto fetched = utils::HttpClient::get(job_url + "&result=1", {}, 120,
+                                          utils::HttpSecurityPolicy::TrustedLoopback);
     if (fetched.status_code != 200) {
         LOG(ERROR, "acestep-server") << "fetching " << stage << " job result failed (HTTP "
                                      << fetched.status_code << ")" << std::endl;

src/cpp/server/backends/cloud/cloud_server.cpp

@@ -737,7 +737,8 @@ void CloudServer::forward_streaming_request(const std::string& endpoint,
 
 std::vector<ModelInfo> CloudServer::discover_models(const std::string& provider,
                                                      const std::string& api_key,
-                                                     const std::string& base_url) {
+                                                     const std::string& base_url,
+                                                     bool allow_insecure_http) {
     std::vector<ModelInfo> models;
     if (api_key.empty()) {
         return models;
@@ -759,13 +760,21 @@ std::vector<ModelInfo> CloudServer::discover_models(const std::string& provider,
         {"Authorization", "Bearer " + api_key}
     };
 
+    // HTTPS providers and remote endpoints use the default external
+    // HTTPS-only policy. Plaintext http:// providers that explicitly set
+    // allow_insecure_http use the AllowInsecureHttp opt-in so http and https
+    // are accepted but redirect chains remain bounded.
+
     utils::HttpResponse response;
     try {
         // Short timeout: this runs synchronously inside cache build, once per
         // configured provider. The 300 s default would block model listing
         // for minutes if a provider's API is unreachable. 15 s is plenty for
         // a /v1/models response under normal conditions.
-        response = utils::HttpClient::get(url, headers, /*timeout_seconds=*/15);
+        response = utils::HttpClient::get(url, headers, /*timeout_seconds=*/15,
+                                          allow_insecure_http
+                                              ? utils::HttpSecurityPolicy::AllowInsecureHttp
+                                              : utils::HttpSecurityPolicy::ExternalHttpsOnly);
     } catch (const std::exception& e) {
         LOG(WARNING, "Cloud") << "Model discovery failed for provider '" << provider
                               << "': " << e.what() << std::endl;
@@ -901,7 +910,8 @@ class CloudOps : public BackendOps {
                 continue;
             }
             try {
-                for (auto& m : CloudServer::discover_models(rec.name, api_key, rec.base_url)) {
+                for (auto& m : CloudServer::discover_models(rec.name, api_key, rec.base_url,
+                                                            rec.allow_insecure_http)) {
                     if (m.recipe == "cloud" && !m.model_name.empty()) {
                         out.push_back(std::move(m));
                     }

src/cpp/server/backends/vllm/vllm_server.cpp

@@ -703,7 +703,8 @@ std::map<std::string, nlohmann::json> VLLMServer::get_additional_telemetry() {
 
     std::string url = "http://127.0.0.1:" + std::to_string(get_backend_port()) + "/metrics";
     try {
-        auto response = utils::HttpClient::get(url, {}, 1);
+        auto response = utils::HttpClient::get(url, {}, 1,
+                                               utils::HttpSecurityPolicy::TrustedLoopback);
         if (response.status_code == 200) {
             return parse_vllm_metrics_text(response.body);
         }

src/cpp/server/model_manager.cpp

@@ -2334,7 +2334,9 @@ size_t ModelManager::refresh_cloud_models(const std::string& provider) {
     // provider and we don't want to block /models on it.
     std::vector<ModelInfo> models;
     try {
-        models = backends::CloudServer::discover_models(provider, api_key, base_url);
+        models = backends::CloudServer::discover_models(
+            provider, api_key, base_url,
+            cloud_registry_->allow_insecure_http_for(provider));
     } catch (const std::exception& e) {
         LOG(WARNING, "ModelManager") << "Cloud discovery threw for provider '"
                                       << provider << "': " << e.what() << std::endl;

src/cpp/server/telemetry.cpp

@@ -410,7 +410,8 @@ class MetricsWorker {
 
             if (!task.metrics_url.empty() && task.parser) {
                 try {
-                    auto response = utils::HttpClient::get(task.metrics_url, {}, 1);
+                    auto response = utils::HttpClient::get(
+                        task.metrics_url, {}, 1, utils::HttpSecurityPolicy::TrustedLoopback);
                     if (response.status_code == 200) {
                         auto extra = task.parser(response.body);
                         for (const auto& [k, v] : extra) {

src/cpp/server/utils/http_client.cpp

@@ -358,9 +358,37 @@ static int progress_callback(void* clientp, curl_off_t dltotal, curl_off_t dlnow
     return 0;
 }
 
+namespace {
+// Applies the scheme and redirect restrictions for a trust boundary. Returns
+// false if any security-relevant option fails to apply so callers can fail
+// closed instead of issuing an unrestricted request.
+bool apply_http_security_policy(CURL* curl, HttpSecurityPolicy policy) {
+    auto set = [curl](CURLoption opt, auto value) {
+        return curl_easy_setopt(curl, opt, value) == CURLE_OK;
+    };
+    switch (policy) {
+        case HttpSecurityPolicy::TrustedLoopback:
+            return set(CURLOPT_FOLLOWLOCATION, 0L) &&
+                   set(CURLOPT_PROTOCOLS_STR, "http");
+        case HttpSecurityPolicy::AllowInsecureHttp:
+            return set(CURLOPT_FOLLOWLOCATION, 1L) &&
+                   set(CURLOPT_MAXREDIRS, 5L) &&
+                   set(CURLOPT_PROTOCOLS_STR, "http,https") &&
+                   set(CURLOPT_REDIR_PROTOCOLS_STR, "http,https");
+        case HttpSecurityPolicy::ExternalHttpsOnly:
+        default:
+            return set(CURLOPT_FOLLOWLOCATION, 1L) &&
+                   set(CURLOPT_MAXREDIRS, 5L) &&
+                   set(CURLOPT_PROTOCOLS_STR, "https") &&
+                   set(CURLOPT_REDIR_PROTOCOLS_STR, "https");
+    }
+}
+} // namespace
+
 HttpResponse HttpClient::get(const std::string& url,
                              const std::map<std::string, std::string>& headers,
-                             long timeout_seconds) {
+                             long timeout_seconds,
+                             HttpSecurityPolicy policy) {
     CURL* curl = curl_easy_init();
     if (!curl) {
         throw std::runtime_error("Failed to initialize CURL");
@@ -372,7 +400,10 @@ HttpResponse HttpClient::get(const std::string& url,
     curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
     curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_callback);
     curl_easy_setopt(curl, CURLOPT_WRITEDATA, &response_body);
-    curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L);
+    if (!apply_http_security_policy(curl, policy)) {
+        curl_easy_cleanup(curl);
+        throw std::runtime_error("Failed to apply HTTP security policy");
+    }
     curl_easy_setopt(curl, CURLOPT_TIMEOUT,
                      timeout_seconds > 0 ? timeout_seconds : default_timeout_seconds_.load());
     curl_easy_setopt(curl, CURLOPT_USERAGENT, "lemon.cpp/1.0");
@@ -651,7 +682,8 @@ DownloadResult HttpClient::download_attempt(const std::string& url,
                                             ProgressCallback callback,
                                             const std::map<std::string, std::string>& headers,
                                             const DownloadOptions& options,
-                                            bool initial_range_request) {
+                                            bool initial_range_request,
+                                            HttpSecurityPolicy policy) {
     DownloadResult result;
 
     CURL* curl = curl_easy_init();
@@ -677,7 +709,12 @@ DownloadResult HttpClient::download_attempt(const std::string& url,
     curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
     curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_file_callback);
     curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp);
-    curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L);
+    if (!apply_http_security_policy(curl, policy)) {
+        result.error_message = "Failed to apply HTTP security policy";
+        fclose(fp);
+        curl_easy_cleanup(curl);
+        return result;
+    }
     curl_easy_setopt(curl, CURLOPT_TIMEOUT, 0L);
     curl_easy_setopt(curl, CURLOPT_USERAGENT, "lemon.cpp/1.0");
     curl_easy_setopt(curl, CURLOPT_CONNECTTIMEOUT, static_cast<long>(options.connect_timeout));
@@ -833,7 +870,12 @@ DownloadResult HttpClient::download_attempt(const std::string& url,
             if (head_curl) {
                 curl_easy_setopt(head_curl, CURLOPT_URL, url.c_str());
                 curl_easy_setopt(head_curl, CURLOPT_NOBODY, 1L);  // HEAD request
-                curl_easy_setopt(head_curl, CURLOPT_FOLLOWLOCATION, 1L);
+                if (!apply_http_security_policy(head_curl, policy)) {
+                    curl_easy_cleanup(head_curl);
+                    result.error_message = "Resume failed (HTTP 416) - could not apply security policy";
+                    result.can_resume = false;
+                    return result;
+                }
                 curl_easy_setopt(head_curl, CURLOPT_TIMEOUT, 30L);
 
                 // Add headers
@@ -899,7 +941,8 @@ DownloadResult HttpClient::download_file(const std::string& url,
                                          const std::string& output_path,
                                          ProgressCallback callback,
                                          const std::map<std::string, std::string>& headers,
-                                         const DownloadOptions& options) {
+                                         const DownloadOptions& options,
+                                         HttpSecurityPolicy policy) {
     DownloadResult final_result;
     int retry_delay_ms = options.initial_retry_delay_ms;
     const ExpectedHash expected_hash = parse_expected_hash(options);
@@ -1022,7 +1065,7 @@ DownloadResult HttpClient::download_file(const std::string& url,
 
         final_result = download_attempt(url, partial_path, resume_offset,
                                         adjusted_callback, headers, options,
-                                        initial_range_request);
+                                        initial_range_request, policy);
 
         // If cancelled by user, return immediately without retrying
         if (final_result.cancelled) {

src/cpp/server/wrapped_server.cpp

@@ -588,7 +588,8 @@ json WrappedServer::forward_get_request(const std::string& endpoint, long timeou
     std::map<std::string, std::string> headers;
 
     try {
-        auto response = utils::HttpClient::get(url, headers);
+        auto response = utils::HttpClient::get(url, headers, 0,
+                                               utils::HttpSecurityPolicy::TrustedLoopback);
         note_backend_activity();
 
         if (response.status_code == 200) {