docs: update custom extensions tutorial #6388

dianed-square · 2026-01-07T23:43:56Z

Summary

This PR removes obsolete version info from the "Building Custom Extensions" topic. Also updates dependency versions.

Documentation updates:

documentation/docs/tutorials/custom-extensions.md:
- Remove protocol version specific link and link to mcp_client.rs file for client info
- Add prereqs
- Update dependency versions and related code fixes
- Separate testing options into tabs
- Update MCP Inspector screenshot and make it clickable

Type of Change

AI Assistance

This PR was created or reviewed with AI assistance

Testing

Manual testing

Related Issues

Closes #6226

To see the specific tasks where the Asana app for GitHub is being used, see below:
- https://app.asana.com/0/0/1212559736671759

github-actions · 2026-01-07T23:46:42Z

PR Preview Action v1.6.3
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2026-01-08 00:50 UTC

Copilot

Pull request overview

This PR updates the "Building Custom Extensions" tutorial to improve clarity and accuracy. The update removes obsolete protocol version information and modernizes dependency versions while enhancing the tutorial structure.

Key changes:

Updated to reference mcp_client.rs for current protocol version info instead of linking to a specific dated specification
Added comprehensive prerequisites section covering Python 3.13+, uv, and Node.js/npm requirements
Reorganized testing instructions into tabbed interface for MCP Inspector vs CLI approaches
Updated dependency versions (beautifulsoup4 4.14.0, html2text 2025.4.15, mcp[cli] 1.25.0) with corresponding code fixes for ErrorData constructor

documentation/docs/tutorials/custom-extensions.md

Copilot · 2026-01-07T23:47:11Z

documentation/docs/tutorials/custom-extensions.md

+        headers = {
+            'User-Agent': 'MCP-Wiki/1.0 (Educational purposes; Python requests)'
+        }
+        response = requests.get(url, headers=headers, timeout=10)


The read_wikipedia_article function calls requests.get(url, ...) on a URL that appears to be user-controlled and only checks that it starts with http, which creates a server-side request forgery (SSRF) risk. An attacker who can invoke this MCP tool could supply an internal or metadata service URL (for example, pointing at cloud instance metadata or internal admin endpoints) and have the server fetch and return sensitive data. To mitigate this, parse the URL and enforce an explicit allowlist of trusted Wikipedia hostnames (and schemes) and reject or sanitize any other URLs before making the request.

fixed in 019f97b

Copilot

Pull request overview

Copilot reviewed 1 out of 2 changed files in this pull request and generated 2 comments.

documentation/docs/tutorials/custom-extensions.md

Copilot · 2026-01-08T00:32:00Z

documentation/docs/tutorials/custom-extensions.md

+        # SSRF protection: only allow Wikipedia domains
+        parsed = urlparse(url)
+        if not parsed.netloc.endswith('wikipedia.org'):
+            raise ValueError(f"Only Wikipedia URLs are allowed. Got: {parsed.netloc}")
+
+        # Add User-Agent header to avoid 403 from Wikipedia
+        headers = {
+            'User-Agent': 'MCP-Wiki/1.0 (Educational purposes; Python requests)'
+        }
+        response = requests.get(url, headers=headers, timeout=10)


The SSRF protection around requests.get is incomplete because it only checks parsed.netloc.endswith('wikipedia.org'), which will also allow attacker-controlled domains like evilwikipedia.org that are not actually owned by Wikipedia. An attacker could register such a domain, point it at internal or local IPs, and still cause the server to make arbitrary HTTP requests, defeating the intended restriction to Wikipedia. To harden this, strictly validate the host so that only wikipedia.org and its legitimate subdomains are allowed (e.g., by checking for exact match or a .-delimited suffix) and consider additionally constraining allowed schemes and IP ranges.

fixed in 75af242

* 'main' of github.com:block/goose: Fixed fonts (#6389) Update confidence levels prompt injection detection to reduce false positive rates (#6390) Add ML-based prompt injection detection (#5623) docs: update custom extensions tutorial (#6388) fix ResultsFormat error when loading old sessions (#6385) docs: add MCP Apps tutorial and documentation updates (#6384) changed z-index to make sure the search highlighter does not appear on modal overlay (#6386) Handling special claude model response in github copilot provider (#6369) fix: prevent duplicate rendering when tool returns both mcp-ui and mcp-apps resources (#6378) fix: update MCP Apps _meta.ui.resourceUri to use nested format (SEP-1865) (#6372) feat(providers): add streaming support for Google Gemini provider (#6191) Blog: edit links in mcp apps post (#6371) fix: prevent infinite loop of tool-input notifications in MCP Apps (#6374)

* main: (31 commits) added validation and debug for invalid call tool result (#6368) Update MCP apps tutorial: fix _meta structure and version prereq (#6404) Fixed fonts (#6389) Update confidence levels prompt injection detection to reduce false positive rates (#6390) Add ML-based prompt injection detection (#5623) docs: update custom extensions tutorial (#6388) fix ResultsFormat error when loading old sessions (#6385) docs: add MCP Apps tutorial and documentation updates (#6384) changed z-index to make sure the search highlighter does not appear on modal overlay (#6386) Handling special claude model response in github copilot provider (#6369) fix: prevent duplicate rendering when tool returns both mcp-ui and mcp-apps resources (#6378) fix: update MCP Apps _meta.ui.resourceUri to use nested format (SEP-1865) (#6372) feat(providers): add streaming support for Google Gemini provider (#6191) Blog: edit links in mcp apps post (#6371) fix: prevent infinite loop of tool-input notifications in MCP Apps (#6374) fix: Show platform-specific keyboard shortcuts in UI (#6323) fix: we load extensions when agent starts so don't do it up front (#6350) docs: credit HumanLayer in RPI tutorial (#6365) Blog: Goose Lands MCP Apps (#6172) Claude 3.7 is out. we had some harcoded stuff (#6197) ...

* main: (89 commits) fix(google): treat signed text as regular content in streaming (#6400) Add frameDomains and baseUriDomains CSP support for MCP Apps (#6399) fix(ci): add missing dependencies to openapi-schema-check job (#6367) feat: http proxy support Add support for changing working dir and extensions in same window/session (#6057) Sort keys in canonical models (#6403) added validation and debug for invalid call tool result (#6368) Update MCP apps tutorial: fix _meta structure and version prereq (#6404) Fixed fonts (#6389) Update confidence levels prompt injection detection to reduce false positive rates (#6390) Add ML-based prompt injection detection (#5623) docs: update custom extensions tutorial (#6388) fix ResultsFormat error when loading old sessions (#6385) docs: add MCP Apps tutorial and documentation updates (#6384) changed z-index to make sure the search highlighter does not appear on modal overlay (#6386) Handling special claude model response in github copilot provider (#6369) fix: prevent duplicate rendering when tool returns both mcp-ui and mcp-apps resources (#6378) fix: update MCP Apps _meta.ui.resourceUri to use nested format (SEP-1865) (#6372) feat(providers): add streaming support for Google Gemini provider (#6191) Blog: edit links in mcp apps post (#6371) ...

update custom extensions tutorial

934852a

Copilot AI review requested due to automatic review settings January 7, 2026 23:43

dianed-square requested a review from a team as a code owner January 7, 2026 23:43

Copilot started reviewing on behalf of dianed-square January 7, 2026 23:44 View session

blackgirlbytes approved these changes Jan 7, 2026

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Copilot AI reviewed Jan 7, 2026

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dianed-square added 2 commits January 7, 2026 16:26

ssrf fix

019f97b

remove trailing whitespace

8f2095f

Copilot AI review requested due to automatic review settings January 8, 2026 00:28

Copilot started reviewing on behalf of dianed-square January 8, 2026 00:29 View session

Copilot AI reviewed Jan 8, 2026

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hardened ssrf

75af242

dianed-square merged commit 01da90c into main Jan 8, 2026
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dianed-square deleted the docs/update-custom-extensions branch January 8, 2026 00:49

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