GHSA-jq8v-rmf6-65jw Gogs has Stored XSS in `.ipynb` Preview

• Go gogs.io/gogs: < 0.14.3 → fixed in 0.14.3

Summary Although `.ipynb` previews are sanitized on the server side via `/-/api/sanitize_ipynb`, the inserted content is re-rendered on the client side without sanitization using `marked()` on elements with the `.nb-markdown-cell` class. During this process, links containing schemes such as `javascript:` can be regenerated. As a result, when a victim views an attacker-crafted `.ipynb` file and clicks the link, arbitrary JavaScript is executed in the Gogs origin, leading to a click-based Stored XSS. Details After the rendered output of a `.ipynb` file is sanitized via `/-/api/sanitize_ipynb` and inserted into the DOM, only the Markdown cell portions are re-rendered using `marked()` and overwritten in the DOM. During this process, links with the `javascript:` scheme can be regenerated. `templates/repo/view_file.tmpl:42–71` ```html {{else if .IsIPythonNotebook}} $.getJSON("{{.RawFileLink}}", null, function(notebook_json) { var notebook = nb.parse(notebook_json); var rendered = notebook.render(); $.ajax({ type: "POST", url: '{{AppSubURL}}/-/api/sanitize_ipynb', data: rendered.outerHTML, processData: false, contentType: false, }).done(function(data) { $("#ipython-notebook").append(data); $("#ipython-notebook code").each(function(i, block) { $(block).addClass("py").addClass("python"); hljs.highlightBlock(block); }); // Overwrite image method to append proper prefix to the source URL var renderer = new marked.Renderer(); var context = '{{.RawFileLink}}'; context = context.substring(0, context.lastIndexOf("/")); renderer.image = function (href, title, text) { return ` ``` While regular HTML pages (including `.ipynb` preview pages) are served without a Content Security Policy (CSP), CSP headers are applied only to attachment delivery routes. `internal/cmd/web.go:323` ```go c.Header().Set("Content-Security-Policy", "default-src 'none'; style-src 'unsafe-inline'; sandbox") ``` Steps to Reproduce 1. As the attacker, add and push/commit a `.ipynb` file containing a `javascript:` link in a Markdown cell to a repository. • Example (PoC): ```json { "nbformat": 4, "nbformat_minor": 2, "metadata": {}, "cells": { "cell_type": "markdown", "metadata": {}, "source": [ "[poc)" ] } ] } ``` 2. The victim opens the file on Gogs (e.g., `///src//poc.ipynb`). 3. When the victim clicks the `poc` link displayed in the preview, `alert(document.domain)` is executed in the same Gogs origin. Minimum Required Privileges • Attacker: Ability to place a `.ipynb` file as a regular (non-admin) user • For example: a general user who can create a public repository and add files. • Or: write access (collaborator, etc.) to an existing repository that the victim will view. • Victim: Permission to view the repository (a click is required). Impact • Unauthorized actions performed with the victim’s account privileges (e.g., repository settings changes, Issue operations,誘導 to token creation). • Theft of information accessible to the victim (repository/Issue/Wiki contents, tokens exposed in page context). • If the victim is an administrator, the impact may escalate to instance-wide configuration changes and user management.