Executive Summary

[{'type': 'paragraph', 'content': 'CVE-2026-29778 is an arbitrary file write vulnerability in the pyload-ng package, specifically in the edit_package() function. This function tries to sanitize the pack_folder parameter to prevent directory traversal attacks by replacing "../" sequences once. However, this single-pass replacement can be bypassed using crafted recursive traversal sequences like "..././..././..././tmp", which after normalization become paths that escape the intended directory.'}, {'type': 'paragraph', 'content': 'As a result, an attacker with authenticated access and MODIFY permissions can write files to arbitrary locations on the system, such as the /tmp directory, potentially modifying files outside the allowed storage area.'}] [1]

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Impact Analysis

[{'type': 'paragraph', 'content': 'This vulnerability allows an attacker with authenticated MODIFY permissions to write files to arbitrary locations on the system, which can lead to unauthorized modification of files (high integrity impact).'}, {'type': 'paragraph', 'content': "Such unauthorized file writes can be exploited to alter application behavior, inject malicious code, or disrupt system operations, potentially compromising the affected system's integrity and reliability."}, {'type': 'paragraph', 'content': 'The attack can be performed remotely with low complexity and does not require user interaction, increasing the risk of exploitation.'}] [1]

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Compliance Impact

I don't know

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Detection Guidance

[{'type': 'paragraph', 'content': 'This vulnerability involves an arbitrary file write via path traversal in the edit_package() function of pyload-ng, specifically through crafted payloads in the pack_folder parameter.'}, {'type': 'paragraph', 'content': "Detection can focus on monitoring for suspicious requests or inputs containing recursive traversal sequences such as '..././..././..././' which bypass the single-pass '../' sanitization."}, {'type': 'paragraph', 'content': 'Since exploitation requires an authenticated user with MODIFY permissions, reviewing logs for unusual modification attempts or unexpected file writes outside the intended directories can help detect exploitation.'}, {'type': 'paragraph', 'content': 'Suggested commands to detect potential exploitation attempts include searching application logs or request logs for patterns like:'}, {'type': 'list_item', 'content': 'grep -r "..././..././" /path/to/pyload/logs'}, {'type': 'list_item', 'content': 'grep -r "pack_folder" /path/to/pyload/logs | grep "..././"'}, {'type': 'list_item', 'content': 'Monitoring file system changes outside the expected directories, for example using:'}, {'type': 'list_item', 'content': "find / -type f -newermt 'YYYY-MM-DD' -exec ls -l {} \\;"}, {'type': 'paragraph', 'content': 'Additionally, network monitoring tools can be configured to alert on suspicious payloads containing recursive traversal sequences in HTTP requests.'}] [1]

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Mitigation Strategies

The primary mitigation step is to upgrade pyload-ng to version 0.5.0b3.dev97 or later, where the vulnerability has been patched.

Until the upgrade can be applied, restrict MODIFY permissions to trusted users only, as exploitation requires authenticated users with such privileges.

Implement additional input validation or sanitization on the pack_folder parameter to prevent recursive traversal sequences.

Monitor logs and file system activity for signs of exploitation attempts and respond accordingly.

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