👻Snapchat Lens Studio: Staging Bug

Snapchat Lens Studio allows developers to "Build, Preview, and Distribute AR" experiences to Snapchat users. I have identified a bug that allows users to take advantage of the 'Preview' function.

GitHub - reidanb/Snapchat-Camera-Roll-Stealth-FilterGitHub

🕵️‍♂️ Discovery of the Issue

This bug was discovered during routine exploration of Snapchat’s Lens Studio and its mobile pairing behaviour, specifically the lens preview pipeline between the desktop editor and a paired device.

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⚙️ Environment Observed

• Platform: Windows 11 with Lens Studio v4.x

• Tools:

  • Lens Studio (AR development environment)

  • Snapchat mobile app (paired via QR code)

  • Process Hacker (portable memory inspection)

  • Python script for replaying preview calls

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🔍 Motivation

While exploring how Lens Studio communicates with the Snapchat app for previewing AR lenses, I noticed a potentially unintended behaviour: content sent via the preview lens mechanism did not enforce any filter overlay or verification on the mobile side. This raised a question:

Is it possible to spoof content via the preview flow using local files from the camera roll?

This hypothesis was tested with the following approach.

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🧪 Methodology

1. Lens Studio login A Snapchat account was authenticated via the official Lens Studio client.

2. Pairing initiated A Snapcode was scanned to pair the mobile Snapchat app with the desktop instance.

3. Live memory inspection Using Process Hacker, I inspected memory for identifiers associated with the session. This led to the discovery of serial_uuid and encryption_key values stored in plain text.

4. Manual payload crafting After extracting the UUID, I examined the web requests used by Lens Studio to send preview data to Snapchat’s API. A multipart form with three files (lens_resource.zip, metadata, and icon_file) was being posted to a staging endpoint.

5. Python proof-of-concept A script was written to replicate this request using the serial_uuid, simulating the same upload flow with custom local content, bypassing Lens Studio entirely.

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📈 Outcome

The mobile device successfully received a "lens preview", which in reality was just user-supplied media repackaged using Snapchat’s infrastructure. The expected AR content was missing because none was actually attached, but Snapchat did not reject the preview due to the valid session ID.

This confirmed:

• No watermarking or source validation

• No enforcement of signed or official lens packages

• Replayable session tokens (at least temporarily)

• Users able to upload camera roll material, posing as taken 'live'. No watermark or otherwise note it was 'uploaded from camera roll' or 'remixed'.

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📌 Implications

This bug allows:

• Unmarked media to be sent through a legitimate Snapchat delivery mechanism

• Potential abuse for impersonation or spam

• Violation of Snapchat’s expected content integrity

This behaviour is not documented or intended and poses a moderate security and policy risk. A formal disclosure was considered, but due to the public accessibility of these endpoints and tools, documentation was prioritised instead.

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📄 Related Diagram

Diagram showing web requests to Snapchat to push the Lens via the Development Ingress API

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✅ Recommendation

Snap Inc. should consider:

• Token expiration or scoping for preview sessions

• Digital signing of preview payloads

• Mobile app validation of incoming media structure

Until addressed, users should be aware of the risks in preview-based AR sharing.