Flask-Reuploaded: Extension-denylist bypass via case-folding asymmetry in name-override path (incomplete-fix variant of CVE-2026-27641)

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-54567
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-14 18:17:53 UTC
Updated2026-09-16 16:17:09 UTC
DescriptionFlask-Reuploaded provides file uploads for Flask. From 1.5.0 until 1.6.0, UploadSet.save(storage, name=...) in src/flask_uploads/flask_uploads.py applies lowercase_ext to the default upload path but uses the case-preserving extension helper for a caller-supplied name before extension_allowed evaluates an AllExcept denylist. An attacker who controls the name override can use a mixed-case dangerous extension to bypass a lowercase denylist and store the file in the served upload directory. Exploitation requires a denylist configuration, a user-influenced name override, and a deployment that resolves or executes extensions case-insensitively; pure allowlists remain protected and path containment is not bypassed. On an execution-capable upload directory, the stored file can execute with the web server's privileges and affect confidentiality, integrity, and availability. This issue is fixed in version 1.6.0.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from [email protected]

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

EPSS: 0.005840000 probability, percentile 0.463550000 (date 2026-09-16)

Problem Types: CWE-178 | CWE-434 | CWE-178 CWE-178: Improper Handling of Case Sensitivity | CWE-434 CWE-434: Unrestricted Upload of File with Dangerous Type

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.5HIGHCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED7.5HIGHCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Jugmac00 Flask-reuploaded affected < 1.6.0 Not specified

References

ReferenceSourceLinkTags
github.com/jugmac00/flask-reuploaded/security/advisories/GHSA-937x-gpqr-... 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
github.com/jugmac00/flask-reuploaded/commit/5ded76092429c6eb8a4af941b14f... [email protected] github.com
github.com/jugmac00/flask-reuploaded/pull/186 [email protected] github.com
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