Arbitrary File Write in Crawl4AI

Executive Summary

CVE-2026-57571 is a vulnerability in Crawl4AI, an open-source web crawler and scraper. Before version 0.9.0, when the crawler saved a downloaded file, it used a filename derived from attacker-controlled input without restricting the file path. This allowed an attacker to specify filenames with absolute paths or directory traversal sequences, escaping the intended downloads directory.

As a result, an attacker could write arbitrary files with attacker-controlled content anywhere on the file system accessible to the crawler. This arbitrary file write could be exploited to escalate to remote code execution.

The issue was fixed in version 0.9.0 by properly confining the filename to the downloads directory.

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Impact Analysis

This vulnerability can have severe impacts including allowing an attacker to write arbitrary files on the system running Crawl4AI.

Because the attacker controls the contents of the written files, they can potentially execute arbitrary code remotely, leading to full system compromise.

Such an exploit could result in data loss, unauthorized access, service disruption, or further attacks within the affected environment.

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Mitigation Strategies

The vulnerability is fixed in Crawl4AI version 0.9.0. Immediate mitigation involves upgrading the Crawl4AI software to version 0.9.0 or later.

Until the upgrade is applied, avoid running the vulnerable versions in untrusted environments or exposing them to untrusted users, as the vulnerability allows arbitrary file writes and potential remote code execution.

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Compliance Impact

This vulnerability allows an attacker to write arbitrary files with controlled content anywhere on the system, potentially leading to remote code execution. Such unauthorized access and control over system files can lead to breaches of confidentiality, integrity, and availability of data.

Because the vulnerability can be exploited remotely and may allow attackers to overwrite critical files, it poses significant risks to data protection and system security, which are core requirements in standards like GDPR and HIPAA.

Failure to address this vulnerability could result in non-compliance with these regulations due to potential unauthorized data access, data manipulation, or service disruption.

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Detection Guidance

This vulnerability can be detected by monitoring for suspicious file writes outside the intended downloads directory of the Crawl4AI crawler, especially files created with names containing absolute paths or directory traversal sequences such as "../" or starting with "/".

You can check your system for unexpected files created by the crawler in locations outside the designated downloads directory, which may indicate exploitation attempts.

Suggested commands to detect potential exploitation include:

• Find files modified or created recently outside the downloads directory that might have been written by the crawler:
• find / -type f -mtime -7 -exec ls -l {} + 2>/dev/null
• Search for files with suspicious names containing traversal sequences:
• find /path/to/downloads -name "*..*" -o -name "/*"
• Monitor crawler logs or network traffic for URLs containing traversal patterns or unusual Content-Disposition headers.

Additionally, ensure you are running version 0.9.0 or later, which includes the fix. If not, consider running the crawler as an unprivileged user with an isolated downloads directory and enable authentication on the Docker server to reduce risk.

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