{"id":"GHSA-g5vh-55hw-rxm8","revision":"ecfd0c65149f465ea9a59ac47a50a1b4","records":[{"revision":"ecfd0c65149f465ea9a59ac47a50a1b4","observedAt":"2026-10-24T13:19:41.952+00:00","statement":{"source":"osv","id":"GHSA-g5vh-55hw-rxm8","aliases":["CVE-2026-44332","GO-2026-5886"],"title":"GoFiber Vulnerable to Username Enumeration via Timing Oracle in BasicAuth Default Authorizer","description":"## 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","state":0,"publishedAt":"2026-07-02T13:46:25+00:00","modifiedAt":"2026-07-24T19:11:49.4530339+00:00","affected":[{"ecosystem":"Go","name":"github.com/gofiber/fiber/v3","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0"},{"kind":"fixed","version":"3.3.0"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[{"system":"CVSS_V3","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N","score":null,"severity":null},{"system":"Publisher rating","vector":null,"score":null,"severity":"MODERATE"}],"references":["https://github.com/gofiber/fiber/security/advisories/GHSA-g5vh-55hw-rxm8","https://github.com/gofiber/fiber"],"sourceUrl":"https://github.com/advisories/GHSA-g5vh-55hw-rxm8","license":"GitHub Advisory Database · CC-BY-4.0","key":"osv:GHSA-g5vh-55hw-rxm8","identifiers":["GHSA-g5vh-55hw-rxm8","CVE-2026-44332","GO-2026-5886"]},"retained":false,"historicalAffected":[]}],"coverage":[]}