CVE-2021-32708

Time-of-check Time-of-use (TOCTOU) Race Condition in league/flysystem

Workarounds

For 1.x users, upgrade to 1.1.4. For 2.x users, upgrade to 2.1.1.

The whitespace normalisation using in 1.x and 2.x removes any unicode whitespace. Under certain specific conditions this could potentially allow a malicious user to execute code remotely.

The conditions:

• A user is allowed to supply the path or filename of an uploaded file.
• The supplied path or filename is not checked against unicode chars.
• The supplied pathname checked against an extension deny-list, not an allow-list.
• The supplied path or filename contains a unicode whitespace char in the extension.
• The uploaded file is stored in a directory that allows PHP code to be executed.

Given these conditions are met a user can upload and execute arbitrary code on the system under attack.

CVE-2021-32708 has a CVSS score of 9.8 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.1.4, 2.1.1); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

The unicode whitespace removal has been replaced with a rejection (exception).

The library has been patched in:

• 1.x: https://github.com/thephpleague/flysystem/commit/f3ad69181b8afed2c9edf7be5a2918144ff4ea32
• 2.x: https://github.com/thephpleague/flysystem/commit/a3c694de9f7e844b76f9d1b61296ebf6e8d89d74

1. What is CVE-2021-32708? CVE-2021-32708 is a critical-severity security vulnerability in league/flysystem (composer), affecting versions < 1.1.4. It is fixed in 1.1.4, 2.1.1.
2. How severe is CVE-2021-32708? CVE-2021-32708 has a CVSS score of 9.8 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of league/flysystem are affected by CVE-2021-32708? league/flysystem (composer) versions < 1.1.4 is affected.
4. Is there a fix for CVE-2021-32708? Yes. CVE-2021-32708 is fixed in 1.1.4, 2.1.1. Upgrade to this version or later.
5. Is CVE-2021-32708 exploitable, and should I be worried? Whether CVE-2021-32708 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2021-32708 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2021-32708?
   • Upgrade league/flysystem to 1.1.4 or later
   • Upgrade league/flysystem to 2.1.1 or later