CVE-2026-8467 Unauthenticated remote code execution via HEEx template injection in phoenix_storybook playground
Unauthenticated attackers can execute arbitrary code on the server by injecting Elixir expressions into HEEx templates via the playground WebSocket handler.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-8467?
CVE-2026-8467 is a critical code injection vulnerability in phenixdigital phoenix_storybook, published on 20 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-94
Which versions are affected by CVE-2026-8467?
3 open source packages ship an affected version, including phoenix_storybook.
| Package | Affected | Fixed in |
|---|---|---|
phoenix_storybook Hex | From 0.5.0 | 1.1.0 |
phoenix_storybook Hex | From 0.5.0 | 1.1.0 |
phoenix_storybook Hex | From 0.5.0 | 1.1.0 |
How do I fix CVE-2026-8467?
Upgrade phoenix_storybook to 1.1.0 or later.
Upgrade, and never evaluate templates, expressions or code built from user input. More about Code injection.
Is CVE-2026-8467 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-8467 exists.
Public exploit code: 1 proofs of concept on GitHub.
Sources
Also known as EEF-CVE-2026-8467, GHSA-55hg-8qxv-qj4p.