Security: DOM-based XSS via unsanitized innerHTML with remote Markdown#627
Open
barttran2k wants to merge 1 commit intooffa:masterfrom
Open
Conversation
The page fetches Markdown from a remote GitHub URL and renders it directly into the DOM using `innerHTML = marked.parse(data)`. The `marked` library does not sanitize HTML by default in many versions. If the remote README.md content is compromised or contains malicious HTML/JavaScript (e.g., via a compromised contributor account), arbitrary scripts could execute in visitors' browsers. Affected files: index.html Signed-off-by: Trần Bách <45133811+barttran2k@users.noreply.github.com>
offa
reviewed
Apr 7, 2026
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Problem
The page fetches Markdown from a remote GitHub URL and renders it directly into the DOM using
innerHTML = marked.parse(data). Themarkedlibrary does not sanitize HTML by default in many versions. If the remote README.md content is compromised or contains malicious HTML/JavaScript (e.g., via a compromised contributor account), arbitrary scripts could execute in visitors' browsers.Severity:
highFile:
index.htmlSolution
Enable DOMPurify or a similar HTML sanitizer after marked parsing:
document.querySelector('main').innerHTML = DOMPurify.sanitize(marked.parse(data));. Alternatively, configure marked with{sanitize: true}(deprecated) or use a sanitizer library like DOMPurify.Changes
index.html(modified)Testing