Time-of-check Time-of-use (TOCTOU) Race Condition in league/flysystem
Impact
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.
Patches
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
Workarounds
For 1.x users, upgrade to 1.1.4. For 2.x users, upgrade to 2.1.1.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Composer package | league/flysystem | < 1.1.4, >= 2.0.0, < 2.1.1 | 1.1.4, 2.1.1 |
References
- https://github.com/thephpleague/flysystem/security/advisories/GHSA-9f46-5r25-5wfm
- https://nvd.nist.gov/vuln/detail/CVE-2021-32708
- https://github.com/thephpleague/flysystem/commit/a3c694de9f7e844b76f9d1b61296ebf6e8d89d74
- https://github.com/thephpleague/flysystem/commit/f3ad69181b8afed2c9edf7be5a2918144ff4ea32
- https://github.com/FriendsOfPHP/security-advisories/blob/master/league/flysystem/CVE-2021-32708.yaml
- https://github.com/thephpleague/flysystem
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/NWPTENBYKI2IG47GI4DHAACLNRLTWUR5
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/RNZSWK4GOMJOOHKLZEOE5AQSLC4DNCRZ
- https://packagist.org/packages/league/flysystem
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H- Weakness (CWE)
CWE-367- Platform
- Composer
- Package
league/flysystem- Disclosed
- 29.06.2021
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-9f46-5r25-5wfm - CC BY 4.0
Vulnerability history: league/flysystem
All published vulnerabilities of this package (Composer package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 2
- First → latest
- 06.2021 09.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 1
- Low 1
Disclosures per year
- 2021: 1
- 2022: 0
- 2023: 0
- 2024: 0
- 2025: 0
- 2026: 1
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Time-of-check Time-of-use (TOCTOU) Race Condition in league/flysystem this entry
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