CVE-2026-102601: Flysystem: WhitespacePathNormalizer's control-character (CorruptedPathDetected) check is bypassed by malformed UTF-8 in the path, affecting every adapter

Severity: low (CVSS 3.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-29 · updated 2026-09-30
Weakness: CWE-150

Description

Flysystem is an open source file storage library for PHP. Prior to 3.35.3, the default WhitespacePathNormalizer in src/WhitespacePathNormalizer.php used by Filesystem across adapters calls preg_match with the u modifier and treats both false and 0 as falsy. A path containing malformed UTF-8 causes PCRE to return false, so paths that also contain control characters bypass CorruptedPathDetected::forPath() in normalizePath(). Filesystem::write() can store such names and Filesystem::listContents() can return the raw ANSI escape sequences, allowing hidden or spoofed terminal file listings when an administrator displays them. This issue is fixed in version 3.35.3.

Affected products

Packagist League/Flysystem: before 3.35.3; 0.1.0, 0.1.1, 0.1.10, 0.1.11, 0.1.12, 0.1.13 (+250) — fixed in 3.35.3
thephpleague flysystem: before 3.35.3

How to fix

Upgrade to a fixed version: Packagist League/Flysystem 3.35.3. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-102601 or the next vulnerability affects your stack