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

Critical severity GitHub Reviewed Published Jun 23, 2021 in thephpleague/flysystem • Updated Feb 6, 2024

Package

composer league/flysystem (Composer)

Affected versions

< 1.1.4
>= 2.0.0, < 2.1.1

Patched versions

1.1.4
2.1.1

Description

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:

Workarounds

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

References

@frankdejonge frankdejonge published to thephpleague/flysystem Jun 23, 2021
Published by the National Vulnerability Database Jun 24, 2021
Reviewed Jun 24, 2021
Published to the GitHub Advisory Database Jun 29, 2021
Last updated Feb 6, 2024

Severity

Critical

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS score

0.707%
(81st percentile)

Weaknesses

CVE ID

CVE-2021-32708

GHSA ID

GHSA-9f46-5r25-5wfm

Source code

Credits

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