CVE-2026-44332: Fiber: Username Enumeration via Timing Oracle in BasicAuth Default Authorizer

Summary

The default Authorizer function in GoFiber's BasicAuth middleware uses short-circuit evaluation that skips password hash comparison for non-existent usernames. With bcrypt-hashed passwords (the primary use case), the timing difference between a valid and invalid username is approximately 1,000,000:1 (~100ms vs ~100ns), enabling reliable remote username enumeration.

Vulnerable Code

File: middleware/basicauth/config.go, lines 126-138

go if cfg.Authorizer == nil { verifiers := make(map[string]func(string) bool, len(cfg.Users)) for u, hpw := range cfg.Users { v, err := parseHashedPassword(hpw) if err != nil { panic(err) } verifiers[u] = v } cfg.Authorizer = func(user, pass string, fiber.Ctx) bool { verify, ok := verifiers[user] return ok && verify(pass) // line 137: short-circuit skips verify() if user unknown } }

Data Flow

1. Attacker sends Authorization: Basic <base64(candidate:wrongpass)> 2. BasicAuth middleware decodes credentials and calls cfg.Authorizer(user, pass, c) 3. Map lookup verifiers[user] returns ok=false for non-existent users 4. Go && short-circuit: false && verify(pass) returns immediately without calling verify() 5. For valid users, verify(pass) executes bcrypt.CompareHashAndPassword() (line 167: ~100ms at default cost 10) 6. Timing difference: ~100ns (invalid user) vs ~100ms (valid user) = 1,000,000:1 ratio

Timing comparison by hash type:

| Hash Type | Valid User | Invalid User | Ratio | |-----------|-----------|--------------|-------| | bcrypt ($2) | ~100 ms | ~100 ns | 1,000,000:1 | | SHA-512 | ~1-5 us | ~100 ns | 10-50:1 | | SHA-256 | ~1-5 us | ~100 ns | 10-50:1 |

Impact

- Username enumeration: Attacker reliably determines which usernames exist by measuring response latency - Targeted brute force: After enumerating valid usernames, password brute force is focused only on real accounts - Account discovery: In applications where usernames are sensitive (internal tools, admin panels), leaking their existence is itself a security issue

Notes

- Password hash comparisons themselves are timing-safe: subtle.ConstantTimeCompare is used correctly for SHA-256 (line 185), SHA-512 (line 176), and bcrypt uses its own constant-time comparison - The fix is to always execute a dummy hash comparison for unknown users: bcrypt.CompareHashAndPassword(dummyHash, []byte(pass)) and discard the result - This pattern matches CVE-2023-36456 (Authentik timing oracle) and similar findings in other auth libraries