{"id":"CVE-2026-44332","aliases":["GHSA-g5vh-55hw-rxm8","GO-2026-5886"],"url":"https://o3.security/vulnerability/CVE-2026-44332","summary":"Fiber: 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","published":"2026-07-08T19:32:15.113Z","modified":"2026-10-21T02:30:24.488775710Z","cvss":{"score":5.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N"},"epss":{"score":0.00517,"percentile":0.427,"asOf":"2026-09-16"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/gofiber/fiber/v3","fixedVersion":"3.3.0"}],"fix":{"url":"https://github.com/gofiber/fiber/commit/c7ac00edd19f9669b1aebbec6e229658baaa059e","label":"gofiber/fiber@c7ac00e"},"references":[{"type":"WEB","url":"https://github.com/gofiber/fiber/releases/tag/v3.3.0"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/44xxx/CVE-2026-44332.json"},{"type":"ADVISORY","url":"https://github.com/gofiber/fiber/security/advisories/GHSA-g5vh-55hw-rxm8"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-44332"},{"type":"FIX","url":"https://github.com/gofiber/fiber/commit/c7ac00edd19f9669b1aebbec6e229658baaa059e"},{"type":"FIX","url":"https://github.com/gofiber/fiber/pull/4245"},{"type":"PACKAGE","url":"https://github.com/gofiber/fiber"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T02:30:24.488775710Z"}}