Unauthenticated remote code execution via HEEx template injection in phoenix_storybook playground

Summary

Code Injection vulnerability in phenixdigital phoenix_storybook allows unauthenticated remote code execution via unsanitized attribute value interpolation in HEEx template generation. The psb-assign WebSocket event handler in 'Elixir.PhoenixStorybook.Story.PlaygroundPreviewLive':handle_event/3 accepts arbitrary attribute names and values from unauthenticated clients. These values are passed to 'Elixir.PhoenixStorybook.Helpers.ExtraAssignsHelpers':handle_set_variation_assign/3, which stores them verbatim. When rendering, 'Elixir.PhoenixStorybook.Rendering.ComponentRenderer':attributes_markup/1 interpolates binary attribute values directly into a HEEx template string as name="<val>" without escaping double quotes or HEEx expression delimiters. An attacker can supply a value containing a closing quote followed by a HEEx expression block (e.g. foo" injected={EXPR} bar="), which causes EXPR to be treated as an inline Elixir expression. The resulting template is compiled via EEx.compile_string/2 and executed via Code.eval_quoted_with_env/3 with full Kernel imports and no sandbox, giving the attacker arbitrary code execution on the server. This issue affects phoenix_storybook from 0.5.0 before 1.1.0.

Timeline

1. May 20, 2026, 1:35 PM UTCCVE published
2. May 21, 2026, 1:57 PM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: yes · Technical impact: total

3. May 27, 2026, 3:41 PM UTCRecord last updated

Affected versions

• phoenix_storybook

  From 0.5.0 · fixed in 1.1.0

• phenixdigital/phoenix_storybook

  Version range not reported

References 5