CVE-2026-33686: Sharp is Vulnerable to Path Traversal via Unsanitized Extension in FileUtil

Summary A path traversal vulnerability exists in the FileUtil class of the code16/sharp package. The application fails to sanitize file extensions properly, allowing path separators to be passed into the storage layer.

Detail In src/Utils/FileUtil.php, the FileUtil::explodeExtension() function extracts a file's extension by splitting the filename at the last dot. However, the extracted extension is never sanitized. While the application uses a normalizeName() function, this function only cleans the base filename, meaning any path separators (such as /) injected into the extension will survive and be passed into the storeAs() function.

Impact Exploiting this flaw allows an authenticated attacker to manipulate file paths: - Files can be written outside of the intended tmp directory via path traversal. For more details on the package, visit: https://github.com/code16/sharp - Existing critical files (such as .env or configuration files) could potentially be overwritten. Review the CWE definition here: https://cwe.mitre.org/data/definitions/22.html (Note: This vulnerability was successfully chained with CWE-434 in a local Proof of Concept to confirm the traversal.)

Patches This issue has been patched by properly sanitizing the extension using pathinfo(PATHINFOEXTENSION) instead of strrpos(), alongside applying strict regex replacements to both the base name and the extension. The fix is available in pull request #715

Credits Reported by zaurgsynv.