PT-2026-41409 · Npm · @Tdurieux/Anonymous Github

Published

2026-05-05

·

Updated

2026-05-05

CVSS v3.1

8.1

High

VectorAV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

Summary

Anonymous GitHub fetches repository content (e.g., markdown files) from GitHub's API and renders it without sanitization. On the client side, markdown is parsed with marked (with sanitize: false) and injected into the DOM via $sce.trustAsHtml() + ng-bind-html, bypassing AngularJS's built-in XSS protection. An attacker can craft a malicious GitHub repository whose README executes arbitrary JavaScript in the Anonymous GitHub origin.

Details

README fetched from GitHub API

The server fetches the README via GitHub's REST API and stores the raw markdown in MongoDB:
typescript
// https://github.com/tdurieux/anonymous github/blob/b2d77faa6c6f35ad9ae6ed46e3a3fa4681ac84c2/src/core/source/GitHubRepository.ts#L162-L174
const ghRes = await oct.repos.getReadme({
 owner: this.owner,
 repo: this.repo,
 ref: selected?.commit,
});
const readme = Buffer.from(
 ghRes.data.content,
 ghRes.data.encoding as BufferEncoding
).toString("utf-8");
selected.readme = readme;
await model.save();
It is then served to the client with no sanitization:
typescript
// https://github.com/tdurieux/anonymous github/blob/b2d77faa6c6f35ad9ae6ed46e3a3fa4681ac84c2/src/server/routes/repository-private.ts#L254-L260
return res.send(
 await repo.readme({
  accessToken: token,
  force: req.query.force == "1",
  branch: req.query.branch as string,
 })
);

Client-side rendering via $sce.trustAsHtml() + ng-bind-html

The client fetches the raw README, parses it with renderMD() (which uses marked with sanitize: false), then bypasses AngularJS sanitization:
javascript
// https://github.com/tdurieux/anonymous github/blob/b2d77faa6c6f35ad9ae6ed46e3a3fa4681ac84c2/public/script/app.js#L1219-L1226
const res = await $http.get(`/api/repo/${o.owner}/${o.repo}/readme`, {
 params: { force: force === true ? "1" : "0", branch: $scope.source.branch },
});
$scope.readme = res.data;
javascript
// https://github.com/tdurieux/anonymous github/blob/b2d77faa6c6f35ad9ae6ed46e3a3fa4681ac84c2/public/script/app.js#L1339-L1343
const html = renderMD(
 $scope.anonymize readme,
 `https://github.com/${o.owner}/${o.repo}/raw/${$scope.source.branch}/`
);
$scope.html readme = $sce.trustAsHtml(html); // sink: bypasses Angular XSS protection
The renderMD() function explicitly disables sanitization:
javascript
// https://github.com/tdurieux/anonymous github/blob/b2d77faa6c6f35ad9ae6ed46e3a3fa4681ac84c2/public/script/utils.js#L165-L176
marked.setOptions({
 sanitize: false, // HTML in markdown is preserved as-is
 // ...
});
return marked.parse(md, { renderer });
The resulting HTML is bound to the DOM via ng-bind-html, which trusts the string marked by $sce.trustAsHtml() and inserts it as innerHTML.

Impact

  1. Stored XSS: Any malicious GitHub repository can execute JavaScript in the Anonymous GitHub origin when a user anonymizes it or views its content
  2. Account Takeover: Steal authentication tokens and session cookies
  3. Data Exfiltration: Access other users' anonymization configurations and private repository data via /api/user and /api/repo/list

Proof of Concept

poc-xss-anonymous-github
  1. Create a GitHub repository with a malicious README.md:
markdown
# Innocent README
<img src=x onerror="alert(document.domain)">
  1. On Anonymous GitHub, enter the malicious repository URL to anonymize it
  2. The XSS executes immediately when the README preview is rendered on the anonymize page

Remediation

  1. Sanitize markdown output with DOMPurify before rendering (the dependency already exists but is unused)
  2. Serve HTML files with Content-Disposition: attachment or in a sandboxed iframe on a separate origin
  3. Replace $sce.trustAsHtml() with proper ngSanitize usage
  4. HTML-escape filenames and paths in directory listing templates
  5. Add Content Security Policy headers

Credits

Zhengyu Liu, Jingcheng Yang

Fix

XSS

Found an issue in the description? Have something to add? Feel free to write us 👾
dbugs@ptsecurity.com

Weakness Enumeration

CWE-80CWE-79

Related Identifiers

GHSA-G485-8J3V-P6X8

Affected Products

@Tdurieux/Anonymous Github