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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

9.8 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS

• CVE-2021-32708: 3.49% estimated exploitation activity in the next 30 days; percentile 89.14 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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:…

Published by the source

29 Jun 2021, 03:13 UTC

Last modified by the source

6 Feb 2024, 13:16 UTC

Source last checked

26 Oct 2026, 14:15 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-9f46-5r25-5wfm

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# Patch Next advisory brief: CVE-2021-32708

Advisory: Time-of-check Time-of-use (TOCTOU) Race Condition in league/flysystem
IDs: CVE-2021-32708, GHSA-9f46-5r25-5wfm
Record: https://patchnext.com/advisories/cve-2021-32708 (revision 1, source checked 26 Oct 2026, 14:15 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: league/flysystem 2.1.1, 1.1.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist league/flysystem: affected < 1.1.4; >= 2.0.0, < 2.1.1; fixed in 1.1.4, 2.1.1

## Suggested inspection (read-only)
- Packagist league/flysystem: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on league/flysystem.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-9f46-5r25-5wfm (GitHub-reviewed advisory GHSA-9f46-5r25-5wfm lists affected ranges: Packagist league/flysystem >=0 =2.0.0 <2.1.1)

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