{"id":"CVE-2026-91972","aliases":["GHSA-6rvj-qwjf-3m4q","GO-2026-6721"],"url":"https://o3.security/vulnerability/CVE-2026-91972","summary":"Vikunja before 2.6.0 Authentication Bypass via Unthrottled API","details":"### Summary\n`registerAPIRoutesV2` never applies the unconditional pre-auth rate-limit floor (`unauthRateLimit()`) to the v2 public routes — it passes that limiter only to `/api/v2/ws` — and otherwise relies on `setupRateLimit`, which registers nothing when `ratelimit.enabled` is false (the default). So on a stock install every v2 pre-auth endpoint (login, register, password-reset token, oauth token) is unthrottled, while its v1 twin is throttled.\n\n### Details\n`unauthRateLimit()` -> `perMinuteIPRateLimit(\"noauth\", RateLimitNoAuthRoutesLimit)` (`pkg/routes/rate_limit.go`, ~lines 100-118) is an unconditional per-IP floor (default 10/60s) that deliberately ignores `RateLimitEnabled`, which is why v1's pre-auth routes are throttled even with the global limiter off. v1 applies it: `ur := a.Group(\"\"); ur.Use(unauthRateLimit())` (`pkg/routes/routes.go` ~line 459). `registerAPIRoutesV2` (~lines 405-431) passes the `unauthRateLimit()` instance only to `/api/v2/ws`; its auth routes get only `setupRateLimit(a, ...)`, which is config-gated and registers nothing by default.\n\n### PoC (verified at runtime against v2.5.0)\n```\nPOST /api/v1/login              x25 -> 429 from attempt 5\nPOST /api/v2/login              x25 -> 403 x25, 429 x0\nPOST /api/v1/user/password/token     -> 429 (throttled)\nPOST /api/v2/user/password/token x20 -> 404 x20, 429 x0\n```\nRequest bodies are byte-identical across versions (shared `user.Login` / `user.PasswordTokenRequest`). Both v2 endpoints reach their handlers (403/404, not route-404), so the comparison is valid.\n\n### Impact\nThe pre-auth rate-limit floor — the instance's only default anti-brute-force / anti-abuse control — is absent on all v2 public endpoints. Enables unbounded credential guessing, account-enumeration probing, and password-reset flooding on a default install. Reported as an authentication-control bypass, not a DoS.\n\n### Fix\nApply `unauthRateLimit()` to the v2 public route group, matching v1.","published":"2026-09-15T15:18:22.792Z","modified":"2026-10-28T02:31:08.740568657Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"Go","name":"code.vikunja.io/api","fixedVersion":"2.6.0"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/91xxx/CVE-2026-91972.json"},{"type":"ADVISORY","url":"https://github.com/go-vikunja/vikunja/security/advisories/GHSA-6rvj-qwjf-3m4q"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-91972"},{"type":"ADVISORY","url":"https://www.vulncheck.com/advisories/vikunja-before-2.6.0-authentication-bypass-via-unthrottled-api"},{"type":"PACKAGE","url":"https://github.com/go-vikunja/vikunja"},{"type":"WEB","url":"https://github.com/go-vikunja/vikunja/releases/tag/v2.6.0"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:31:08.740568657Z"}}