Clarification Request: Standardized Guidance for Detecting Malicious Patterns in Widget HTML

Open
#664 0 comments 0 reactions 0 assignees View on GitHub

Nobody has claimed this yet.

Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
48/100
Issue type
Documentation
Clarity
Mostly clear
Activity status
Quiet
Tech stack
html
Domain
documentation, security

Research direction

Start with specification/2026-01-26/apps.mdx around the Host behaviour guidance linked in the issue. Review the existing wording and document a consistent baseline for malicious-pattern detection, including the expected host response; done means the security expectation is explicit while preserving legitimate widget compatibility.

Written by the indexing model from the issue text.

Description

The current guidance mentions Host behaviour should:

https://github.com/modelcontextprotocol/ext-apps/blob/9a37ad71827d076af06978fa7f7f510449687061/specification/2026-01-26/apps.mdx?plain=1#L1718

Could we clarify whether there is a standardized guideline or recommended policy for what should be considered a “malicious pattern” in the context of hosted/embedded widgets?

Specifically:

  • Is there an existing standard list or definition of patterns that hosts are expected to scan for?

  • Are there recommended categories of suspicious content (for example, script injection, inline event handlers, javascript: URLs, unexpected iframe usage, etc.)?

  • Is the expectation that hosts implement:

    • strict blocking,
    • best-effort heuristic scanning,
    • or logging/telemetry only?

Context

For third-party widgets/apps, full HTML sanitization is often not practical because it can break legitimate functionality. It would be helpful to understand whether there is a common baseline guideline that hosts should follow for detecting clearly malicious content without overly restricting valid widget behavior.
Goal
Align host implementations on a consistent security expectation while preserving compatibility for legitimate third-party widgets.

Dominant language
TypeScript
Stars
2.9k
Forks
387
Avg merge
3h 21m
Merged PRs (30d)
6

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from modelcontextprotocol/ext-apps

All issues in modelcontextprotocol/ext-apps

Similar issues

More TypeScript issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.