EEF-CVE-2026-94206

Cloak PBKDF2 field ignores the configured iteration count and runs only :size rounds

## Summary Use of Password Hash With Insufficient Computational Effort vulnerability in danielberkompas cloak_ecto and danielberkompas cloak allows an attacker who holds the hashed values and the configured secret to brute-force low-entropy plaintexts much faster than configured. The `dump/1` callback that `Cloak.Ecto.PBKDF2` (`Cloak.Fields.PBKDF2` in cloak before the Ecto code moved to cloak_ecto) injects into a field module calls `:pbkdf2.pbkdf2/4` with `config[:size]` in the iteration-count position. The `:iterations` setting is validated but never used. With the cloak_ecto defaults (`iterations: 600_000`, `size: 32`) each hash runs 32 PBKDF2 rounds instead of 600,000, so offline guessing of values such as email addresses costs about 18,750 times less than configured. This issue affects cloak_ecto: from 1.0.0-alpha.0 onward; cloak: from 0.7.0 before 1.0.0-alpha.0. ## Proof of concept 1. Define a field module with `use Cloak.Ecto.PBKDF2` and configure only a `:secret`, so that the defaults `iterations: 600_000` and `size: 32` apply. 2. Call `dump/1` on a value. 3. Compare the result with `:pbkdf2.pbkdf2({:hmac, :sha256}, value, secret, 32)` and with the same call at 600,000 rounds. It matches the 32-round hash, not the 600,000-round hash, and returns in microseconds instead of about one second. ## Impact An attacker who obtains a database dump and the PBKDF2 secret can recover hashed values with low entropy, such as email addresses, by offline guessing at a cost far below what the configuration promises. ## Workarounds Override `dump/1` in the field module that uses `Cloak.Ecto.PBKDF2`, so that it calls `:pbkdf2.pbkdf2/5` with the configured `:iterations` and `:size`. Then recompute all stored hashes, because the existing values no longer match.