# 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.

- **Severity:** Critical 9.5 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 20 May 2026
- **Updated:** 27 May 2026
- **Also known as:** EEF-CVE-2026-8467, GHSA-55hg-8qxv-qj4p

## 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 (Improper Control of Generation of Code)

## Which versions are affected by CVE-2026-8467?

3 open source packages ship an affected version, including phoenix_storybook.


| Package | Ecosystem | 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.

## 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:

- CVE-2026-8467 - Draft or TODO (github_poc): https://github.com/HORKimhab/CVE-2026-8467

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-8467 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-8467 exists.

Affected packages and fixed versions:
- phoenix_storybook (Hex): affected from 0.5.0; fixed in 1.1.0
- phoenix_storybook (Hex): affected from 0.5.0; fixed in 1.1.0
- phoenix_storybook (Hex): affected from 0.5.0; fixed in 1.1.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-8467/ (Markdown: https://insights.sbomify.com/CVE-2026-8467/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-8467
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-8467
- OSV: https://osv.dev/vulnerability/CVE-2026-8467

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-8467/
Summaries are generated and may contain mistakes; the official description above is the record.