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Fencer Vulns
critical 9.5

CVE-2026-8467 json

Unauthenticated remote code execution via HEEx template injection in phoenix_storybook playground

published 2026-05-20 5 mo ago modified 2026-07-30 3 mo ago also EEF-CVE-2026-8467 , GHSA-55hg-8qxv-qj4p , EUVD-2026-31112

cvss
9.5
version 4.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
2.1%
EPSS 2.1% chance of exploitation in 30 days, percentile 81%
public exploits
0
none known

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.

Patch / fix

  • hex phoenix_storybook 1.1.0
  • phenixdigital phoenix_storybook 1.1.0

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
total
Assessed
5 mo ago

Exploit prediction

2.11% chance of exploitation in the next 30 days, higher than 81% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/phenixdigital/phoenix_storybook/security/advisories/GHSA-55hg-8qxv-qj4p referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 4.0 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
CNA 4.0 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected packages

ecosystem package affected fixed in
hex phoenix_storybook
>=0.5.0, <1.1.0
1.1.0

Affected products

  • phenixdigital phoenix_storybook

Classification

Weakness
  • CWE-94 Improper Control of Generation of Code

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.