CVE-2024-21644

ExploitedNVD CIRCL ENISA

EUVD-2024-0387 · Published Jan 8, 2024

pyload Unauthenticated Flask Configuration Leakage vulnerability

Summary

Any unauthenticated user can browse to a specific URL to expose the Flask config, including the SECRET_KEY variable.

Details

Any unauthenticated user can browse to a specific URL to expose the Flask config, including the SECRET_KEY variable.

PoC

Run pyload in the default configuration by running the following command

pyload

Now browse to http://localhost:8000/render/info.html. Notice how the Flask configuration gets displayed.
PoC

I was quite amused by this finding. I think it's a very interesting coming together of things that is so unlikely to happen. Below I will detail my process a bit more.

I was looking through the code to see how the authorization mechanism is implemented when I spotted this route, which can be accessed by any unauthenticated actor

https://github.com/pyload/pyload/blob/57d81930edb59177c60830ad8ac36a91d0ec4c4e/src/pyload/webui/app/blueprints/app_blueprint.py#L33C1-L37C51

@bp.route("/render/<path:filename>", endpoint="render")
def render(filename):
    mimetype = mimetypes.guess_type(filename)[0] or "text/html"
    data = render_template(filename)
    return flask.Response(data, mimetype=mimetype)

This route allows me to load in any of the predefined templates. However, these templates will be lacking any form of context, and as such it doesn't seem too useful. That is until I loaded the info.html template and scrolled down, revealing the Flask config. This was purely accidental, and I did not understand why it happened, until I looked at the template

https://github.com/pyload/pyload/blob/57d81930edb59177c60830ad8ac36a91d0ec4c4e/src/pyload/webui/app/templates/info.html#L64C1-L67C10

    <tr>
        <td>{{ _("Config folder:") }}</td>
        <td>{{ config }}</td>
    </tr>

In Flask, every template always gets the Flask config passed to it as the config variable. In the normal execution of this template, this value gets overwritten in the function below, but since we're calling it and bypassing this function altogether, it doesn't get overwritten. Would this variable not be named config and named configuration or Config instead, then this exploit wouldn't work. The likelihood of this occurring is so small, but it seems to have happened here.

https://github.com/pyload/pyload/blob/57d81930edb59177c60830ad8ac36a91d0ec4c4e/src/pyload/webui/app/blueprints/app_blueprint.py#L450C1-L461C51

    context = {
        "python": sys.version,
        "os": " ".join((os.name, sys.platform) + extra),
        "version": api.get_server_version(),
        "folder": PKGDIR,
        "config": api.get_userdir(),
        "download": conf["general"]["storage_folder"]["value"],
        "freespace": format.size(api.free_space()),
        "webif": conf["webui"]["port"]["value"],
        "language": conf["general"]["language"]["value"],
    }
    return render_template("info.html", **context)

Impact

Depending on the how the Flask config data is used, it could have detrimental consequences for the security. It's crucial to keep the SECRET_KEY secret and never expose it in your code or configuration files.

Technologies

Pyload PyloadPyload-Ng Pyload-Ng

Weaknesses

CWE-284

CVSS scores

v3.17.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

MITRE ATT&CK

Inferred

Where this vulnerability fits in an attack

ReconImpact

Initial Access

T1190Exploit Public-Facing Application

References

Potentially impacted assets

See if this affects your attack surface

Latest trending attack

Criticalyesterday

Google Brotli decoder - Remote Code Execution via compressed requests (Exploitation Check)

This control is the second step of the Patrowl response to CVE-2026-111497 (Node2Shell). It complements the first control of 22 October 2026, which focused on the Node.js runtime, and does not replace it. Why a second control CVE-2026-111497 is an out-of-bounds write in the Google Brotli decoder, the library that decompresses Brotli ("br") data. It was first published as a Node.js vulnerability, because Node.js bundles this decoder. Later publications showed that the flaw is in the library itself. Every product that embeds an affected version of the decoder is concerned, whatever its language or vendor. A public proof of concept demonstrates code execution. Any server that decompresses request bodies sent with "Content-Encoding: br" exposes the decoder to unauthenticated attackers. Known cases include Express 5 and NestJS 11 on Node.js, Koa and Fastify setups, Bun, Envoy and Istio with request decompression enabled, and any application or reverse proxy that decodes Brotli request bodies with an affected library. The flaw also works in the other direction. A malicious server can compromise an unpatched client that decodes a Brotli response, for example Node.js fetch(), Python clients (requests, httpx, aiohttp, Scrapy) with the Brotli or brotlicffi package, or libcurl builds with Brotli support. What this control checks Patrowl sends small, valid Brotli-compressed requests to each asset and observes whether the server decodes them. The check does not depend on the technology: it detects the behaviour, whatever the stack behind it. These requests are what any legitimate client could send. They never reach the vulnerable code path and cannot affect the availability of the service. How to read the result Potentially impacted means the asset decodes Brotli request bodies: the attack surface is exposed. It does not confirm that the asset is vulnerable. The version of the Brotli decoder in use is not visible from the outside. This check covers applications that parse request bodies on their root path. A Not impacted result does not rule out exposure on other routes, nor on the client side. Checking the versions on the servers remains the only exhaustive verification. Affected and fixed versions Google Brotli 1.0.3 to 1.2.0 are affected, fixed in 1.0.10, 1.1.1 and 1.2.1. Fixed releases of the main products embedding it: Node.js 22.23.4, 24.22.1 and 26.12.1 (end-of-life lines 20.x and older and 25.x receive no fix), Bun 1.4.4, Envoy 1.37.8, 1.38.6, 1.39.3 and 1.40.0, Istio 1.29.9, 1.30.6 and 1.31.2, Python Brotli 1.2.1 and brotlicffi 1.2.1.0. Products that link against the system library depend on the Brotli package of the Linux distribution. Recommendations Update every component that embeds the Brotli decoder (only real fix). Start with the assets flagged by this control. Restart the processes after the update. Rebuild containers, single-executable applications and appliances that bundle an affected runtime or library. Reduce the exposure until the update is deployed. Reject requests with "Content-Encoding: br" at the reverse proxy, load balancer or WAF, case-insensitively and including lists such as "gzip, br". On Envoy and Istio, disable request decompression for Brotli. Review outbound calls. List the features that fetch content from servers you do not control, and patch the services that host them first.