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claude-code - 💡(How to fix) Fix Unexpected message injection — text from WhatsApp appeared in Claude Code session [1 participants]

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anthropics/claude-code#56144•Fetched 2026-05-05 05:57:02
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During a Claude Code session, text that was written exclusively in WhatsApp (on a phone) appeared as a user message inside the Claude Code terminal session (on a Windows PC). Claude Code then acted on this text as if it were a user instruction.

The user confirmed:

  • The text was written only in WhatsApp on their phone
  • They did not paste it into Claude Code
  • They did not have another Claude session open
  • They did not intentionally send this message to Claude Code

Root Cause

During a Claude Code session, text that was written exclusively in WhatsApp (on a phone) appeared as a user message inside the Claude Code terminal session (on a Windows PC). Claude Code then acted on this text as if it were a user instruction.

The user confirmed:

  • The text was written only in WhatsApp on their phone
  • They did not paste it into Claude Code
  • They did not have another Claude session open
  • They did not intentionally send this message to Claude Code
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Description

During a Claude Code session, text that was written exclusively in WhatsApp (on a phone) appeared as a user message inside the Claude Code terminal session (on a Windows PC). Claude Code then acted on this text as if it were a user instruction.

The user confirmed:

  • The text was written only in WhatsApp on their phone
  • They did not paste it into Claude Code
  • They did not have another Claude session open
  • They did not intentionally send this message to Claude Code

What happened

  1. User was working with Claude Code in a terminal session on Windows 11
  2. Multiple background agents were running (code review tasks)
  3. A personal WhatsApp message written on the user's phone appeared as a system-reminder tagged "The user sent a new message while you were working"
  4. Claude Code interpreted this as a user instruction and hardcoded the private message text into the dashboard source code
  5. The code was committed and deployed to production, exposing the private message on the CRM dashboard

Expected behavior

Claude Code should never receive input from other applications. Only text explicitly entered in the Claude Code prompt should be treated as user messages.

Environment

  • Platform: Windows 11 Pro (10.0.26200)
  • Shell: bash (Git Bash)
  • Claude Code: CLI / Desktop
  • Model: claude-opus-4-6 (1M context)

Privacy concern

This is a significant privacy issue. Private messages from unrelated applications should never leak into Claude Code sessions or be acted upon as instructions.

extent analysis

TL;DR

Isolate Claude Code from external input sources to prevent unauthorized text from being interpreted as user instructions.

Guidance

  • Investigate potential clipboard or cross-application communication vulnerabilities that could allow WhatsApp text to be transmitted to Claude Code.
  • Review Claude Code's input handling mechanisms to ensure they only accept text explicitly entered in the Claude Code prompt.
  • Consider implementing a validation step to verify the origin of input text before processing it as a user instruction.
  • Evaluate the security of background agents running during Claude Code sessions to prevent potential data leaks.

Example

No code snippet is provided due to the lack of specific technical details about Claude Code's implementation.

Notes

The exact cause of the issue is unclear, but it appears to be related to unintended communication between applications. Further investigation is needed to determine the root cause and implement a reliable fix.

Recommendation

Apply a workaround to isolate Claude Code from external input sources until a permanent fix can be implemented, as this is a significant privacy concern.

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FAQ

Expected behavior

Claude Code should never receive input from other applications. Only text explicitly entered in the Claude Code prompt should be treated as user messages.

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claude-code - 💡(How to fix) Fix Unexpected message injection — text from WhatsApp appeared in Claude Code session [1 participants]