{"id":"CVE-2026-54567","summary":"Flask-Reuploaded: Extension-denylist bypass via case-folding asymmetry in name-override path (incomplete-fix variant of CVE-2026-27641)","details":"Flask-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.","aliases":["GHSA-937x-gpqr-72gg","PYSEC-2026-3466"],"modified":"2026-09-18T03:30:37.771872094Z","published":"2026-09-14T17:15:49.272Z","database_specific":{"cwe_ids":["CWE-178","CWE-434"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/54xxx/CVE-2026-54567.json","unresolved_ranges":[{"extracted_events":[{"fixed":"1.6.0"}],"source":"AFFECTED_FIELD"}],"cna_assigner":"GitHub_M"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/54xxx/CVE-2026-54567.json"},{"type":"ADVISORY","url":"https://github.com/jugmac00/flask-reuploaded/security/advisories/GHSA-937x-gpqr-72gg"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-54567"},{"type":"FIX","url":"https://github.com/jugmac00/flask-reuploaded/commit/5ded76092429c6eb8a4af941b14fbde40a38fff4"},{"type":"FIX","url":"https://github.com/jugmac00/flask-reuploaded/pull/186"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/jugmac00/flask-reuploaded","events":[{"introduced":"0"},{"fixed":"5ded76092429c6eb8a4af941b14fbde40a38fff4"}],"database_specific":{"source":"REFERENCES"}}],"versions":["0.2.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-54567.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H"}]}