CVE-2026-91973

### Summary The `/dav`, `/.well-known`, and `/feeds` groups are registered on the root Echo instance with only BasicAuth and no rate limiter. CalDAV BasicAuth accepts the plain account password, so password guessing over `/dav` is unbounded and never returns 429, while `/api/v1/login` is throttled from the tenth attempt. The only anti-brute-force control on the instance is therefore bypassable. ### Details `pkg/routes/routes.go` (~lines 238-249) registers `/.well-known`, `/dav`, and `/feeds` with `middleware.BasicAuth(...)` and nothing else; `registerCalDavRoutes` adds no limiter. `pkg/routes/caldav/auth.go` (~lines 88-93) falls through to `user.CheckUserCredentials` with the plain account password when no CalDAV token matches. In contrast, `/register`, `/login`, etc. are wrapped by `unauthRateLimit()` — an unconditional 10/min/IP pre-auth floor that ignores `ratelimit.enabled` (default false). TOTP-enabled accounts and bot users are correctly refused, so this targets password-only accounts. ### PoC (verified at runtime against v2.5.0) ``` POST /api/v1/login x25 wrong passwords -> 429 from attempt 2 (throttled) PROPFIND /dav/principals/{user}/ x60 wrong passwords -> 401 x60, 429 x0 GET /feeds/notifications.atom x30 wrong passwords -> 401 x30, 429 x0 PROPFIND /dav/... with correct password -> 207 (proves the 401s are real auth failures) ``` ### Impact The anti-brute-force floor guarding `/login` is entirely absent on `/dav`, `/feeds`, and `/.well-known`, giving an unbounded credential-guessing surface against account passwords. (bcrypt caps throughput to a few guesses/second, but nothing caps the number of attempts.) Reported as an authentication-control bypass, not a DoS. ### Fix Apply the unconditional pre-auth rate-limit floor to the `/dav`, `/.well-known`, and `/feeds` groups.

Vikunja: CalDAV and feeds BasicAuth endpoints have no rate limit, bypassing the anti-brute-force floor on account passwords in code.vikunja.io/api. NOTE: The source advisory for this report contains additional versions that could not be automatically mapped to standard Go module versions. (If this is causing false-positive reports from vulnerability scanners, please suggest an edit to the report.) The additional affected modules and versions are: code.vikunja.io/api before v2.6.0.