Anki Localhost API File Read via Malicious Iframe

Executive Summary

This vulnerability exists in Anki versions prior to 25.09.4. Anki uses a webview-based interface that communicates with its Rust backend through an internal localhost API. User scripts included via iframes in the editor are supposed to be blocked from accessing this API, but due to the vulnerability, they can still access it.

A malicious imported card package containing an embedded iframe can exploit this flaw by using exposed API methods such as getImageForOcclusion to read arbitrary files accessible to the Anki process and send them over the network.

This issue was fixed in Anki version 25.09.4.

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Impact Analysis

The vulnerability allows a malicious card package to read arbitrary files accessible to the Anki process and exfiltrate them over the network.

This can lead to unauthorized disclosure of sensitive or personal data stored or accessible by Anki on the affected system.

The CVSS score of 6.5 indicates a medium severity impact, with high confidentiality impact but no impact on integrity or availability.

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Mitigation Strategies

To mitigate this vulnerability, you should update Anki to version 25.09.4 or later, where the issue has been fixed.

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Compliance Impact

The vulnerability allows a malicious imported card package to read arbitrary files accessible to the Anki process and exfiltrate them over the network. This unauthorized access and potential data exfiltration could lead to exposure of sensitive personal or protected information.

Such exposure may impact compliance with data protection regulations like GDPR or HIPAA, which require safeguarding personal and sensitive data against unauthorized access and disclosure.

However, the provided information does not explicitly discuss compliance implications or specific regulatory impacts.

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Detection Guidance

This vulnerability can be detected by monitoring for unexpected outbound network requests originating from the Anki application, especially after importing untrusted .apkg files. Since the exploit involves malicious iframes accessing Anki's internal localhost API and exfiltrating files over the network, observing unusual network traffic from Anki is a key indicator.

Additionally, inspecting the contents of imported .apkg files for embedded iframes or suspicious user scripts before importing can help detect potential exploitation attempts.

Suggested commands to detect suspicious activity include:

• On Linux/macOS, use network monitoring tools like tcpdump or lsof to detect outbound connections from Anki:
• tcpdump -i any -n host not 127.0.0.1 and port 80 or port 443
• lsof -i -a -c anki
• On Windows, use Resource Monitor or PowerShell commands to monitor network activity for the Anki process.
• To inspect .apkg files (which are zip archives), use unzip or similar tools to extract and review HTML/JS content for embedded iframes:
• unzip -l deck.apkg
• unzip deck.apkg -d extracted_deck
• Then search for iframe tags or suspicious scripts within the extracted files.

Blocking unexpected outbound network requests from Anki at the firewall level is also recommended as a mitigation and detection measure.

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