{"schema_version":"1.9.0","id":"GHSA-g5vh-55hw-rxm8","published":"2026-07-02T13:46:25Z","modified":"2026-07-24T19:11:49.453033906Z","aliases":["CVE-2026-44332","GO-2026-5886"],"summary":"GoFiber Vulnerable to Username Enumeration via Timing Oracle in BasicAuth Default Authorizer","details":"## Summary\n\nThe 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.\n\n## Vulnerable Code\n\n**File:** `middleware/basicauth/config.go`, lines 126-138\n\n```go\nif cfg.Authorizer == nil {\n    verifiers := make(map[string]func(string) bool, len(cfg.Users))\n    for u, hpw := range cfg.Users {\n        v, err := parseHashedPassword(hpw)\n        if err != nil {\n            panic(err)\n        }\n        verifiers[u] = v\n    }\n    cfg.Authorizer = func(user, pass string, _ fiber.Ctx) bool {\n        verify, ok := verifiers[user]\n        return ok && verify(pass)   // line 137: short-circuit skips verify() if user unknown\n    }\n}\n```\n\n## Data Flow\n\n1. Attacker sends `Authorization: Basic <base64(candidate:wrongpass)>`\n2. BasicAuth middleware decodes credentials and calls `cfg.Authorizer(user, pass, c)`\n3. Map lookup `verifiers[user]` returns `ok=false` for non-existent users\n4. Go `&&` short-circuit: `false && verify(pass)` returns immediately without calling `verify()`\n5. For valid users, `verify(pass)` executes `bcrypt.CompareHashAndPassword()` (line 167: ~100ms at default cost 10)\n6. Timing difference: ~100ns (invalid user) vs ~100ms (valid user) = 1,000,000:1 ratio\n\n**Timing comparison by hash type:**\n\n| Hash Type | Valid User | Invalid User | Ratio |\n|-----------|-----------|--------------|-------|\n| bcrypt ($2) | ~100 ms | ~100 ns | 1,000,000:1 |\n| SHA-512 | ~1-5 us | ~100 ns | 10-50:1 |\n| SHA-256 | ~1-5 us | ~100 ns | 10-50:1 |\n\n## Impact\n\n- **Username enumeration:** Attacker reliably determines which usernames exist by measuring response latency\n- **Targeted brute force:** After enumerating valid usernames, password brute force is focused only on real accounts\n- **Account discovery:** In applications where usernames are sensitive (internal tools, admin panels), leaking their existence is itself a security issue\n\n## Notes\n\n- 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\n- The fix is to always execute a dummy hash comparison for unknown users: `bcrypt.CompareHashAndPassword(dummyHash, []byte(pass))` and discard the result\n- This pattern matches CVE-2023-36456 (Authentik timing oracle) and similar findings in other auth libraries","affected":[{"package":{"name":"github.com/gofiber/fiber/v3","ecosystem":"Go","purl":"pkg:golang/github.com/gofiber/fiber/v3"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"3.3.0"}]}],"database_specific":{"last_known_affected_version_range":"<= 3.2.0","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/07/GHSA-g5vh-55hw-rxm8/GHSA-g5vh-55hw-rxm8.json"}}],"references":[{"type":"WEB","url":"https://github.com/gofiber/fiber/security/advisories/GHSA-g5vh-55hw-rxm8"},{"type":"PACKAGE","url":"https://github.com/gofiber/fiber"}],"database_specific":{"cwe_ids":["CWE-203"],"github_reviewed":true,"github_reviewed_at":"2026-07-02T13:46:25Z","nvd_published_at":null,"severity":"MODERATE"},"severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N"}]}