A critical security risk has emerged for Windows users of WhatsApp Desktop who also have Python installed.
Attackers can exploit a flaw in how WhatsApp Desktop handles .pyz (Python archive) files, delivering arbitrary code execution on the victim’s machine with a single click.
Researchers have discovered that a maliciously crafted .pyz file—normally used to bundle Python applications—can be disguised as an innocuous attachment (for example, named profile_update.pyz) and sent through WhatsApp Desktop’s file transfer feature.
When the user downloads and double-clicks the file, Windows launches the Python interpreter associated with the .pyz extension by default.
Because the archive contains Python bytecode or scripts, it runs without additional prompts or warnings, directly handing control to the attacker.
Technical Details and Attack Scenario
WhatsApp Desktop for Windows registers the .pyz extension to open with the user’s Python installation.
Unlike executables or script files, .pyz archives appear as opaque, single-file packages—making it difficult for non-technical users to distinguish malicious payloads.
An attacker could embed backdoors, ransomware, or credential harvesters inside the archive. Upon execution, the payload could:
- Install persistent services or scheduled tasks
- Harvest stored passwords, tokens, or browser cookies
- Deploy lateral movement tools to compromise other machines on the network
- Exfiltrate sensitive data to remote servers
Since Python is widely installed by developers and power users, many WhatsApp Desktop users are unwittingly at risk.
This attack vector closely mirrors a vulnerability discovered in Telegram Desktop earlier this year. In that instance, Telegram’s Windows client allowed malicious .pyz files to execute without user confirmation.
Telegram issued a patch within days, altering file-handling logic to block Python archives or prompt users before execution. By contrast, WhatsApp Desktop has yet to implement similar safeguards.
Meta, the parent company of WhatsApp, has acknowledged receipt of vulnerability reports but does not currently classify the .pyz behavior as a security flaw.
Official statements assert that Python archives are considered “user-supplied executables,” placing responsibility on end users to avoid clicking unknown attachments.
Security experts argue this stance underestimates the risk posed by file-packing formats that masquerade as benign. Without built-in blocking or warning mechanisms, millions of Windows users remain vulnerable.
Until Meta issues an update, security professionals advise the following precautions:
- Disable automatic opening of .pyz files: Reassign the file association in Windows Settings so that .pyz files do not launch Python by default.
- Use file-type filters: Install endpoint protection tools that block execution of unexpected file formats received via messaging apps.
- Preview before opening: Encourage non-technical users to verify file extensions and scan attachments with antivirus software.
- Update messaging clients: Regularly install the latest version of WhatsApp Desktop, watching for any emergency patches addressing this issue.
The discovery of Python-based code execution in WhatsApp Desktop underscores a growing trend: attackers gravitating toward legitimate developer tools and packaging formats to bypass traditional security controls.
With Meta’s current posture delaying a direct fix, enterprise defenders and home users alike must proactively harden their environments.
Security researchers hope that public awareness and mounting user pressure will compel WhatsApp’s development team to adopt the same preventative measures already applied in Telegram Desktop.
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