PYSEC-2026-3618 Thumbor has path traversal via post-validation URL decoding bypass in file_loader

The fileloader performs unquote on the file path AFTER the abspath + startswith security check. An attacker can use percent-encoded path traversal sequences %2e%2e for .. that pass the security check as literal directory names, but are then decoded to actual .. traversal sequences. Affected code...

Thumbor has path traversal via post-validation URL decoding bypass in file_loader

The fileloader performs unquote on the file path AFTER the abspath + startswith security check. An attacker can use percent-encoded path traversal sequences %2e%2e for .. that pass the security check as literal directory names, but are then decoded to actual .. traversal sequences. Affected...