diff --git a/src/client/client_cli.c b/src/client/client_cli.c
index c00a9f2..0a345a7 100644
--- a/src/client/client_cli.c
+++ b/src/client/client_cli.c
@@ -400,8 +400,8 @@ static bool validate_config(const Config* config) {
     return false;
   }
   if (config->use_tls) {
-    if (!config->tls_cert || !config->tls_key) {
-      fprintf(stderr, "Error: --tls requires --cert and --key\n");
+    if (!config->tls_cert || !config->tls_key || !config->tls_ca) {
+      fprintf(stderr, "Error: --tls requires --cert, --key, and --ca\n");
       return false;
     }
   }
diff --git a/src/server/server.c b/src/server/server.c
index ee34957..6ab4e4f 100644
--- a/src/server/server.c
+++ b/src/server/server.c
@@ -23,6 +23,7 @@
 static char* authorized_root;
 static int authorized_root_fd = -1;
 static bool allow_delete;
+static bool allow_unauthenticated;
 
 static bool path_is_within(const char* root, const char* path) {
   size_t n = strlen(root);
@@ -34,6 +35,15 @@ static bool valid_batch_path(const char* path) {
          strchr(path, '\0') == path + strlen(path);
 }
 
+static bool batch_path_exists_secure(const char* path, const char* root) {
+  char* full_path = path_cat(root, path);
+  if (!full_path)
+    return false;
+  bool exists = file_path_exists_secure(full_path);
+  free(full_path);
+  return exists;
+}
+
 static bool __attribute__((unused)) configure_authorization(const char* root) {
   char resolved[PATH_MAX];
   if (!root || !realpath(root, resolved))
@@ -121,7 +131,8 @@ int receive_files(Config* config, int fd) {
         char* full_path = path_cat(config->receive_root_directory, check_path);
         struct stat st;
         bool has_old = full_path && lstat(full_path, &st) == 0;
-        bool match = has_old && (unsigned long long)st.st_size == check_size &&
+        bool secure_exists = batch_path_exists_secure(check_path, config->receive_root_directory);
+        bool match = has_old && secure_exists && (unsigned long long)st.st_size == check_size &&
                      (long long)st.st_mtime == check_mtime;
         bool sent = send_status(fd, match ? STATUS_OK : STATUS_NEXT);
         free(full_path);
@@ -179,6 +190,12 @@ void handler(int file_descriptor) {
     close(file_descriptor);
     return;
   }
+  if (!allow_unauthenticated && ssl == NULL) {
+    log_message(LOG_LEVEL_ERROR, "Rejected unauthenticated plaintext connection");
+    config_delete(config);
+    close(file_descriptor);
+    return;
+  }
   char resolved_destination[PATH_MAX];
   char* canonical_destination = realpath(config->receive_root_directory, NULL);
   const char* destination =
@@ -283,6 +300,7 @@ static void print_server_usage(void) {
   printf("  --ca <path>         TLS CA certificate file (PEM)\n");
   printf("  --destination-root <path>  Authorized destination root (default: .)\n");
   printf("  --allow-delete      Permit manifest deletion\n");
+  printf("  --allow-unauthenticated  Allow plaintext/anonymous network clients\n");
   printf("  -v, --verbose       Enable debug logging\n");
   printf("  --help              Show this help\n");
 }
@@ -317,6 +335,8 @@ int main(int argc, char* argv[]) {
       destination_root = argv[++i];
     } else if (strcmp(argv[i], "--allow-delete") == 0) {
       allow_delete = true;
+    } else if (strcmp(argv[i], "--allow-unauthenticated") == 0) {
+      allow_unauthenticated = true;
     } else if (strcmp(argv[i], "-p") == 0 && i + 1 < argc) {
       char* end;
       long p = strtol(argv[++i], &end, 10);
@@ -357,8 +377,8 @@ int main(int argc, char* argv[]) {
     return 1;
   }
   if (use_tls) {
-    if (!tls_cert || !tls_key) {
-      fprintf(stderr, "Error: --tls requires --cert and --key\n");
+    if (!tls_cert || !tls_key || !tls_ca) {
+      fprintf(stderr, "Error: --tls requires --cert, --key, and --ca\n");
       server_delete(&g_server);
       return 1;
     }
diff --git a/src/shared/chunk.c b/src/shared/chunk.c
index 4ccf0d5..480342e 100644
--- a/src/shared/chunk.c
+++ b/src/shared/chunk.c
@@ -14,6 +14,7 @@
 
 /* Maximum individual file data size within a chunk (64 MB) */
 #define MAX_FILE_DATA_SIZE (64ULL * 1024 * 1024)
+#define MAX_FILES_PER_CHUNK 65536U
 
 Chunk* chunk_create(File** items, int element_count) {
   Chunk* chunk = (Chunk*)malloc(sizeof(Chunk));
@@ -88,10 +89,17 @@ Data* chunk_serialize(Chunk* chunk, bool use_metadata) {
 
 Chunk* chunk_deserialize(Data* data, bool use_metadata) {
   ArrayList* files = array_list_create(file_destroy);
+  if (files == NULL)
+    return NULL;
   char* data_pointer = data->data;
   size_t remaining_size = data->size;
 
   while (remaining_size > 0) {
+    if ((unsigned int)files->size >= MAX_FILES_PER_CHUNK) {
+      log_message(LOG_LEVEL_ERROR, "Chunk contains too many files");
+      array_list_delete(files);
+      return NULL;
+    }
     if (remaining_size < sizeof(size_t)) {
       log_message(LOG_LEVEL_ERROR, "Invalid chunk format: not enough data for path length");
       array_list_delete(files);
@@ -109,6 +117,10 @@ Chunk* chunk_deserialize(Data* data, bool use_metadata) {
       return NULL;
     }
 
+    if (path_len == SIZE_MAX) {
+      array_list_delete(files);
+      return NULL;
+    }
     char* path = malloc(path_len + 1);
     if (path == NULL) {
       perror("Could not allocate memory for file path");
@@ -117,6 +129,11 @@ Chunk* chunk_deserialize(Data* data, bool use_metadata) {
     }
     memcpy(path, data_pointer, path_len);
     path[path_len] = '\0';
+    if (memchr(path, '\0', path_len) != NULL) {
+      free(path);
+      array_list_delete(files);
+      return NULL;
+    }
     data_pointer += path_len;
     remaining_size -= path_len;
 
@@ -180,7 +197,11 @@ Chunk* chunk_deserialize(Data* data, bool use_metadata) {
     data_pointer += file_data_size;
     remaining_size -= file_data_size;
 
-    array_list_add(files, file);
+    if (!array_list_add(files, file)) {
+      file_destroy(file);
+      array_list_delete(files);
+      return NULL;
+    }
   }
 
   File** file_array = (File**)array_list_to_array(files);
diff --git a/src/shared/config.c b/src/shared/config.c
index 4c1a3a0..529512b 100644
--- a/src/shared/config.c
+++ b/src/shared/config.c
@@ -100,6 +100,33 @@ static void config_set_defaults(Config* config) {
   config->compress_choice = NULL;
 }
 
+static bool valid_wire_bool(int value) {
+  return value == 0 || value == 1;
+}
+
+static bool validate_received_config(const Config* config) {
+  return valid_wire_bool(config->save_to_disk) && valid_wire_bool(config->use_multithreading) &&
+         valid_wire_bool(config->use_chunk_serialization) &&
+         valid_wire_bool(config->use_compression) && valid_wire_bool(config->use_metadata) &&
+         valid_wire_bool(config->use_sendfile) && valid_wire_bool(config->use_delete) &&
+         valid_wire_bool(config->use_incremental) && valid_wire_bool(config->use_delta) &&
+         valid_wire_bool(config->backup) && valid_wire_bool(config->follow_symlinks) &&
+         valid_wire_bool(config->copy_links) && valid_wire_bool(config->safe_links) &&
+         valid_wire_bool(config->copy_unsafe_links) &&
+         valid_wire_bool(config->preserve_hard_links) && valid_wire_bool(config->preserve_acls) &&
+         valid_wire_bool(config->preserve_xattrs) && valid_wire_bool(config->preserve_devices) &&
+         valid_wire_bool(config->preserve_sparse) && valid_wire_bool(config->update) &&
+         valid_wire_bool(config->inplace) && valid_wire_bool(config->append) &&
+         valid_wire_bool(config->append_verify) && valid_wire_bool(config->delete_excluded) &&
+         valid_wire_bool(config->delete_after) && valid_wire_bool(config->relative) &&
+         valid_wire_bool(config->prune_empty_dirs) && valid_wire_bool(config->partial) &&
+         config->compression_level >= 1 && config->compression_level <= 22 &&
+         config->chunk_size > 0 && config->chunk_size <= MAX_CHUNK_SIZE &&
+         config->delta_block_size >= DELTA_BLOCK_SIZE_MIN &&
+         config->delta_block_size <= DELTA_BLOCK_SIZE_MAX &&
+         config->delta_max_file_size <= DELTA_MAX_FILE_SIZE && config->max_delete >= 0;
+}
+
 Config* config_create(void) {
   Config* config = malloc(sizeof(Config));
   if (!config)
@@ -320,18 +347,26 @@ Config* config_receive(int file_descriptor) {
   int tmp;
   if (!receive_int(file_descriptor, &tmp))
     goto error;
+  if (!valid_wire_bool(tmp))
+    goto error;
   config->save_to_disk = tmp;
   if (!receive_int(file_descriptor, &tmp))
     goto error;
+  if (!valid_wire_bool(tmp))
+    goto error;
   config->use_multithreading = tmp;
   if (!receive_int(file_descriptor, &tmp))
     goto error;
   config->use_chunk_serialization = tmp;
   if (!receive_int(file_descriptor, &tmp))
     goto error;
+  if (!valid_wire_bool(tmp))
+    goto error;
   config->use_compression = tmp;
   if (!receive_int(file_descriptor, &tmp))
     goto error;
+  if (!valid_wire_bool(tmp))
+    goto error;
   config->use_metadata = tmp;
   if (!receive_int(file_descriptor, &tmp))
     goto error;
@@ -340,15 +375,23 @@ Config* config_receive(int file_descriptor) {
     goto error;
   if (!receive_int(file_descriptor, &tmp))
     goto error;
+  if (!valid_wire_bool(tmp))
+    goto error;
   config->use_sendfile = tmp;
   if (!receive_int(file_descriptor, &tmp))
     goto error;
+  if (!valid_wire_bool(tmp))
+    goto error;
   config->use_delete = tmp;
   if (!receive_int(file_descriptor, &tmp))
     goto error;
+  if (!valid_wire_bool(tmp))
+    goto error;
   config->use_incremental = tmp;
   if (!receive_int(file_descriptor, &tmp))
     goto error;
+  if (!valid_wire_bool(tmp))
+    goto error;
   config->use_delta = tmp;
   if (!receive_n_data(file_descriptor, &config->delta_block_size, sizeof(config->delta_block_size)))
     goto error;
@@ -440,6 +483,11 @@ Config* config_receive(int file_descriptor) {
     send_status(file_descriptor, STATUS_ERROR);
     goto error;
   }
+  if (!validate_received_config(config)) {
+    fprintf(stderr, "Invalid configuration received from client\n");
+    send_status(file_descriptor, STATUS_ERROR);
+    goto error;
+  }
   if (!send_status(file_descriptor, STATUS_OK))
     goto error;
   return config;
diff --git a/src/shared/delta.c b/src/shared/delta.c
index 26685db..343c0be 100644
--- a/src/shared/delta.c
+++ b/src/shared/delta.c
@@ -36,6 +36,9 @@ DeltaSignature* delta_signature_create(const void* old_file_data, uint64_t old_f
   if (old_file_data == NULL || old_file_size == 0 || block_size == 0)
     return NULL;
 
+  if (old_file_size > DELTA_MAX_FILE_SIZE || old_file_size > UINT32_MAX * (uint64_t)block_size)
+    return NULL;
+
   uint32_t block_count = (uint32_t)((old_file_size + block_size - 1) / block_size);
 
   DeltaSignature* sig = malloc(sizeof(DeltaSignature));
@@ -463,7 +466,8 @@ Delta* delta_deserialize(const Data* data) {
 void* delta_apply(const void* old_data, uint64_t old_size, const Delta* delta,
                   uint32_t block_size) {
   if (!old_data || !delta || (delta->new_file_size > 0 && delta->instructions == NULL) ||
-      (delta->instruction_count > 0 && block_size == 0))
+      (delta->instruction_count > 0 && block_size == 0) ||
+      delta->new_file_size > DELTA_MAX_FILE_SIZE || delta->new_file_size > SIZE_MAX)
     return NULL;
 
   void* output = malloc((size_t)delta->new_file_size);
diff --git a/src/shared/file.c b/src/shared/file.c
index b333ce1..3df95bb 100644
--- a/src/shared/file.c
+++ b/src/shared/file.c
@@ -155,7 +155,24 @@ bool file_send_single_calls(File* file, int file_descriptor, bool use_metadata,
 
 static bool to_disk_secure(const char* path, const void* data, unsigned long long data_size,
                            bool inplace, bool sparse, const FileMetadata* metadata);
-static int open_secure_parent(const char* path, char** leaf_out);
+static int open_secure_parent(const char* path, char** leaf_out, bool create_dirs);
+
+bool file_path_exists_secure(const char* path) {
+  if (!path)
+    return false;
+  char* leaf = NULL;
+  int parent_fd = open_secure_parent(path, &leaf, false);
+  if (parent_fd < 0)
+    return false;
+  struct stat st;
+  int fd = openat(parent_fd, leaf, O_RDONLY | O_CLOEXEC | O_NOFOLLOW);
+  bool exists = fd >= 0 && fstat(fd, &st) == 0;
+  if (fd >= 0)
+    close(fd);
+  close(parent_fd);
+  free(leaf);
+  return exists;
+}
 static bool rename_secure(const char* old_path, const char* new_path);
 static int authorized_root_fd = -1;
 static char* authorized_root_path;
@@ -532,7 +549,7 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
   int old_fd = -1;
   if (full_path) {
     char* leaf = NULL;
-    int parent_fd = open_secure_parent(full_path, &leaf);
+    int parent_fd = open_secure_parent(full_path, &leaf, false);
     if (parent_fd >= 0) {
       old_fd = openat(parent_fd, leaf, O_RDONLY | O_CLOEXEC | O_NOFOLLOW);
       free(leaf);
@@ -542,7 +559,7 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
   }
   unsigned long long old_size = has_old_file ? (unsigned long long)st.st_size : 0;
   void* old_data = NULL;
-  if (has_old_file && old_size > 0) {
+  if (has_old_file && old_size > 0 && old_size <= DELTA_MAX_FILE_SIZE && old_size <= SIZE_MAX) {
     old_data = malloc((size_t)old_size);
     if (old_data) {
       size_t got = 0;
@@ -651,7 +668,7 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
   return file;
 }
 
-static int open_secure_parent(const char* path, char** leaf_out) {
+static int open_secure_parent(const char* path, char** leaf_out, bool create_dirs) {
   char* copy = str_dup(path);
   if (!copy)
     return -1;
@@ -691,7 +708,7 @@ static int open_secure_parent(const char* path, char** leaf_out) {
   while (component) {
     if (strcmp(component, ".") != 0 && strcmp(component, "..") != 0) {
       int next = openat(fd, component, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
-      if (next < 0 && errno == ENOENT && mkdirat(fd, component, 0755) == 0)
+      if (create_dirs && next < 0 && errno == ENOENT && mkdirat(fd, component, 0755) == 0)
         next = openat(fd, component, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
       if (next < 0) {
         close(fd);
@@ -711,8 +728,8 @@ static int open_secure_parent(const char* path, char** leaf_out) {
 
 static bool rename_secure(const char* old_path, const char* new_path) {
   char *old_leaf = NULL, *new_leaf = NULL;
-  int old_parent = open_secure_parent(old_path, &old_leaf);
-  int new_parent = open_secure_parent(new_path, &new_leaf);
+  int old_parent = open_secure_parent(old_path, &old_leaf, true);
+  int new_parent = open_secure_parent(new_path, &new_leaf, true);
   bool ok = old_parent >= 0 && new_parent >= 0 &&
             renameat(old_parent, old_leaf, new_parent, new_leaf) == 0;
   if (old_parent >= 0)
@@ -741,7 +758,7 @@ static bool write_all(int fd, const void* data, unsigned long long size) {
 static bool to_disk_secure(const char* path, const void* data, unsigned long long data_size,
                            bool inplace, bool sparse, const FileMetadata* metadata) {
   char* leaf = NULL;
-  int dirfd = open_secure_parent(path, &leaf);
+  int dirfd = open_secure_parent(path, &leaf, true);
   if (dirfd < 0)
     return false;
   int fd = -1;
diff --git a/src/shared/file.h b/src/shared/file.h
index e763f91..33fbd52 100644
--- a/src/shared/file.h
+++ b/src/shared/file.h
@@ -40,6 +40,7 @@ bool to_disk(const char* path, const void* data, unsigned long long data_size, b
 bool file_save_to_disk(const char* root_directory, const File* file, const Config* config);
 void file_set_authorized_root(int fd, const char* canonical_path);
 File* receive_incremental_check(int fd, const Config* config, bool* skipped);
+bool file_path_exists_secure(const char* path);
 int receive_manifest(int fd, const Config* config, int* next_status);
 
 #endif
diff --git a/src/shared/protocol.c b/src/shared/protocol.c
index a3a3aed..56fb852 100644
--- a/src/shared/protocol.c
+++ b/src/shared/protocol.c
@@ -260,6 +260,11 @@ char* receive_str(int file_descriptor) {
     free(data);
     return NULL;
   }
+  if (memchr(data, '\0', size) != NULL) {
+    free(data);
+    log_message(LOG_LEVEL_ERROR, "Received string contains an embedded NUL");
+    return NULL;
+  }
   data[size] = '\0';
   total_allocated_bytes += size + 1;
   log_message(LOG_LEVEL_DEBUG, "Received String: %s", data);
diff --git a/src/shared/transport_tls.c b/src/shared/transport_tls.c
index 49fc554..2b373ef 100644
--- a/src/shared/transport_tls.c
+++ b/src/shared/transport_tls.c
@@ -11,6 +11,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/socket.h>
+#include <sys/stat.h>
 #include <sys/wait.h>
 #include <unistd.h>
 
@@ -43,8 +44,19 @@ static SSL_CTX* create_ssl_ctx(bool is_server, const char* cert, const char* key
   }
 
   SSL_CTX_set_min_proto_version(ctx, TLS1_2_VERSION);
+  if (SSL_CTX_set_cipher_list(ctx, "HIGH:!aNULL:!eNULL:!MD5:!RC4:!3DES") != 1) {
+    SSL_CTX_free(ctx);
+    return NULL;
+  }
 
   if (cert && key) {
+    struct stat key_stat;
+    if (stat(key, &key_stat) != 0 || !S_ISREG(key_stat.st_mode) || key_stat.st_uid != geteuid() ||
+        (key_stat.st_mode & (S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH))) {
+      log_message(LOG_LEVEL_ERROR, "TLS private key must be owned by the current user and private");
+      SSL_CTX_free(ctx);
+      return NULL;
+    }
     if (SSL_CTX_use_certificate_file(ctx, cert, SSL_FILETYPE_PEM) <= 0) {
       log_message(LOG_LEVEL_ERROR, "Failed to load certificate: %s", cert);
       log_ssl_errors();
diff --git a/tests/integration/common.py b/tests/integration/common.py
index 08cc9c9..2e9653a 100644
--- a/tests/integration/common.py
+++ b/tests/integration/common.py
@@ -25,7 +25,9 @@ class ServerManager:
     def start(self, extra_args=None):
         self.stop()
         self._port = _find_free_port()
-        cmd = SERVER_CMD + ["-p", str(self._port)]
+        # Plain TCP is intentionally explicit in the server; integration tests
+        # exercise that opt-in mode rather than relying on the secure default.
+        cmd = SERVER_CMD + ["-p", str(self._port), "--allow-unauthenticated"]
         if extra_args:
             cmd += extra_args
         self._proc = subprocess.Popen(cmd, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
diff --git a/tests/integration/test_tls.py b/tests/integration/test_tls.py
index 06e8caa..d74ef15 100644
--- a/tests/integration/test_tls.py
+++ b/tests/integration/test_tls.py
@@ -102,6 +102,7 @@ class TestTLSBasic:
         with ServerManager() as server:
             server.start(extra_args=[
                 "--tls", "--cert", certs["server_cert"], "--key", certs["server_key"],
+                "--ca", certs["ca"],
             ])
             result, dur = run_client(
                 SOURCE_DIR, DEST_DIR,
@@ -125,6 +126,7 @@ class TestTLSBasic:
         with ServerManager() as server:
             server.start(extra_args=[
                 "--tls", "--cert", certs["server_cert"], "--key", certs["server_key"],
+                "--ca", certs["ca"],
             ])
             result, dur = run_client(
                 SOURCE_DIR, DEST_DIR,
@@ -149,6 +151,7 @@ class TestTLSBasic:
         with ServerManager() as server:
             server.start(extra_args=[
                 "--tls", "--cert", certs["server_cert"], "--key", certs["server_key"],
+                "--ca", certs["ca"],
             ])
             result, dur = run_client(
                 SOURCE_DIR, DEST_DIR,