GHSA-833p-95jq-929q: PhoenixStorybook: Unbounded atom creation from LiveView event params (atom-table DoS)
SummaryAn attacker who can deliver `psb-assign`, `psb-toggle`, `psb-set-theme`, `upper-tab-navigation`, `lower-tab-navigation`, `playground-change`, or `playground-toggle` LiveView events to a mounted Phoenix Storybook playground can flood the BEAM atom table with attacker-controlled strings, permanently leaking atoms until the VM hits its ~1,048,576 atom ceiling and crashes the entire node. No authentication is required beyond being able to reach the storybook route.Tabs parsing was introduced in https://github.com/phenixdigital/phoenix_storybook/commit/0228669d55c23a754d1ef11f49a32121129d5395Details`PhoenixStorybook.Story.Playground` and `PhoenixStorybook.ExtraAssignsHelpers` converts user-supplied event params into atoms without checking whether the atoms already exist:`handle_set_variation_assign/3` (`lib/phoenix_storybook/helpers/extra_assigns_helpers.ex:59`) iterates the event params map and calls `String.to_atom/1` on every key.`handle_toggle_variation_assign/3` (line 73) calls `String.to_atom/1` on the `"attr"` value supplied by the client.`to_variation_id/2` (lines 90, 93) calls `String.to_atom/1` on each element of `"variation_id"`.`to_value/4` (lines 106, 107) calls `String.to_atom/1` on the raw string value for any attribute declared as `:atom` or `:boolean`.The existing guards do not help: `check_type!/3` for `:boolean` inspects the atom *after* `String.to_atom/1` has already interned it, so the leak has already happened. The `:atom` branch only checks `is_atom/1`, which is trivially true for the atom that was just created. Atoms in the BEAM are never garbage-collected, so each unique attacker string is a permanent leak; once the atom table fills, the VM aborts.The fix is to use `String.to_existing_atom/1` (with a rescue that rejects unknown names) or, better, to look the attribute / variation up in the declared `story.attributes()` / variation registry and reuse the atom from there.PoCThe attached script focuses on only the first class of parameters. It encodes the threat model of an outside attacker who can deliver `psb-assign` events to a mounted storybook playground LiveView. LiveView event handlers route those params into the public helper `PhoenixStorybook.ExtraAssignsHelpers.handle_set_variation_assign/3` (see `lib/phoenix_storybook/live/story/playground_preview_live.ex`), so the script calls that helper directly with attacker-shaped params — a stub `FakeStory` providing an empty `attributes/0` list and a single `:default` variation, plus an `extra_assigns` map keyed by `{:single, :default}`.Each simulated request is a params map with 5,000 unique keys of the form `"psb_evil_<nonce>_<r>_<i>"`. Because the helper does `for {key, value} <- params, ..., do: {String.to_atom(key), ...}`, every distinct key is interned as a brand-new permanent atom. The script issues 5 such requests for 25,000 atoms total — modest on purpose so the script finishes quickly; raising either loop bound walks the process straight into `:erlang.system_info(:atom_limit)` and crashes the VM.The script measures `:erlang.system_info(:atom_count)` before and after, prints the delta and the atom limit, and prints `VERIFIED: …` when the delta is at least `requests * attrs_per_request` (i.e. 25,000), proving that each attacker-controlled string became a permanent atom. No authentication is required by the helper itself — only the ability to reach the storybook route and emit the event.The full script is attached below under "Scripts and Logs".ImpactUnauthenticated denial-of-service via atom-table exhaustion against any Phoenix application that mounts Phoenix Storybook (1.0.0) on a network-reachable route. A single sustained stream of `psb-assign` / `psb-toggle` events with unique keys is enough to crash the entire BEAM node, taking down every application running on it — not just the storybook. The only precondition is reachability of the storybook LiveView; many deployments expose it in staging/preview environments or, by misconfiguration, in production.Scripts and LogsLogs
CVSS v4.0: 8.2