yogthos/markdown-clj

Prevent potential XSS by default

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#188 opened on Oct 12, 2022

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bughelp wanted

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Description

Example markdown:

[click me](javascript:window.onerror=alert;throw%20document.URL)

Markdown clj will render:

Maybe we force folks to specify specific protocols they want to support and validate the urls? We just discovered this and haven't done much analysis at this point.

This is what other popular Java markdown tools do:

https://github.com/commonmark/commonmark-java/blob/main/commonmark/src/main/java/org/commonmark/renderer/html/DefaultUrlSanitizer.java

Note, this doesn't affect other online editors either:

https://dillinger.io/ https://stackedit.io/app# https://jbt.github.io/markdown-editor/

Contributor guide

Research direction
Inspect the markdown clj source code to understand how URLs are rendered, then implement a URL sanitizer similar to commonmark java, allowing only safe protocols.
Tech stack
clojure
Domain
security
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Mostly clear
Prerequisites
ClojureHTML
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
75