GHSA-cxf4-7mrp-vvpr Flysystem: WhitespacePathNormalizer's control-character (CorruptedPathDetected) check is bypassed by malformed UTF-8 in the path, affecting every adapter

• Packagist league/flysystem: < 3.35.3 → fixed in 3.35.3

Related public issue (context, not a duplicate) Closed issue #1429 ("Handle non-UTF-8 paths", 2024-03-24) raised exactly this general concern and even suggested detection via `preg_match('//u', $path) !== 1` -- note the reporter's suggested check explicitly compares `!== 1`, which *would* correctly treat PCRE's `false` return as "reject." The maintainer's reply pointed to the `PathNormalizer` interface as the place to implement this. The control-character check that ended up shipping in `WhitespacePathNormalizer` (`if (preg_match('#\p{C}+#u', $unixPath))`) addresses the general concern but does not use the `!== 1`-style comparison the original issue suggested -- it uses a bare truthy check, which is exactly the gap this report demonstrates. So this is not a duplicate of #1429; it's a concrete bypass surviving in the fix that issue's concern led to. Vulnerability Details File: `src/WhitespacePathNormalizer.php`, lines 22-28 (`normalizePath()`) -- the default `PathNormalizer` used by `Filesystem` for every adapter (Local, FTP, SFTP, S3, AsyncAwsS3, Azure, GCS, ZipArchive, GridFS, InMemory) unless the application supplies a custom one. Root Cause ```php public function normalizePath(string $path): string { $unixPath = str_replace('\\', '/', $path); if (preg_match('#\p{C}+#u', $unixPath)) { throw CorruptedPathDetected::forPath($path); } ... ``` `preg_match()` returns `false` (a PHP engine error) rather than `0` when the subject string is not valid UTF-8 and the pattern uses the `/u` modifier -- PCRE can't even attempt the match. `false` and `0` are both falsy in PHP, and `if (preg_match(...))` does not distinguish them. So a path containing any single invalid UTF-8 byte anywhere in the string makes `preg_match()` fail with a "Malformed UTF-8 characters" engine error, the `if` evaluates false, and `CorruptedPathDetected` is silently not thrown -- even when the same string also contains literal control characters this exact check exists to catch. the identical payload IS correctly rejected once it's valid UTF-8: ```php $n->normalizePath("foo\x1bbar"); // valid UTF-8, contains ESC -> throws CorruptedPathDetected (correct) $n->normalizePath("foo\x80\x1bbar"); // 0x80 = invalid lone UTF-8 continuation byte -> NOT thrown (bypass) ``` The path-traversal protection is unaffected -- it's exact byte-string comparison on `/`-delimited segments, independent of UTF-8 validity: ```php $n->normalizePath("\x80/../../etc/passwd"); // still throws PathTraversalDetected ``` Recommended Fix ```php public function normalizePath(string $path): string { $unixPath = str_replace('\\', '/', $path); $matched = preg_match('#\p{C}+#u', $unixPath); if ($matched !== 0) { // $matched === false means malformed UTF-8 -- must also be treated as corrupted, // not silently allowed through. throw CorruptedPathDetected::forPath($path); } ... ``` Verification Dynamically confirmed on `league/flysystem` HEAD `6837e1d` / tag `3.35.2`, PHP 8.4.22 CLI, end-to-end through `LocalFilesystemAdapter`: ``` [1] write() succeeded -- normalizer did NOT reject the path. [2] Actual bytes on disk: ...801b5b386d6e6f726d616c2d6c6f6f6b696e672d66696c652e7478741b5b306d... [3] Filesystem::listContents() path contains raw ESC (0x1b): YES [4] Raw terminal output (via `cat -v`): M-^@^[[8mnormal-looking-file.txt^[[0m^[[2K^[[1Aurgent-invoice.pdf