CVE-2025-25297

EUVD-2025-4107 · Published Feb 14, 2025

Label Studio allows Server-Side Request Forgery in the S3 Storage Endpoint

Description

Label Studio's S3 storage integration feature contains a Server-Side Request Forgery (SSRF) vulnerability in its endpoint configuration. When creating an S3 storage connection, the application allows users to specify a custom S3 endpoint URL via the s3_endpoint parameter. This endpoint URL is passed directly to the boto3 AWS SDK without proper validation or restrictions on the protocol or destination.

The vulnerability allows an attacker to make the application send HTTP requests to arbitrary internal services by specifying them as the S3 endpoint. When the storage sync operation is triggered, the application attempts to make S3 API calls to the specified endpoint, effectively making HTTP requests to the target service and returning the response in error messages.

This SSRF vulnerability enables attackers to bypass network segmentation and access internal services that should not be accessible from the external network. The vulnerability is particularly severe because error messages from failed requests contain the full response body, allowing data exfiltration from internal services.

Steps to reproduce

Create an account in Label Studio
Create a new project with basic configuration

Create an S3 storage connection with the following configuration:

{
  "project": 1,
  "title": "Test Storage",
  "bucket": "<filename>",
  "s3_endpoint": "http://internal-web",
  "use_blob_urls": true,
  "aws_access_key_id": "test",
  "aws_secret_access_key": "test"
}

Trigger a storage sync operation by sending a POST request to /api/storages/s3/[storage_id]/sync

The application will attempt to connect to the specified endpoint URL as if it were an S3 service. When the request fails due to invalid S3 API responses, the error message will contain the raw response from the internal service, allowing access to internal resources.

Mitigations

Implement strict validation of S3 endpoint URLs to allow only valid S3service endpoints
Add an allowlist of endpoint domains and protocols
Sanitize error messages to prevent leakage of sensitive information from failed requests
Consider implementing network-level controls to restrict outbound connections from the application server

Impact

This vulnerability has high severity as it allows authenticated users to make requests to arbitrary internal services from the application server, potentially exposing sensitive internal resources and bypassing network segmentation. The inclusion of response data in error messages makes this particularly effective for data exfiltration.

Technologies

Humansignal Label StudioLabel-Studio Label-Studio

Weaknesses

CWE-918

CVSS scores

v3.18.6CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/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.