CVE-2026-52798 — gogs.io/gogs
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')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
{{else if .IsIPythonNotebook}}
<script>
$.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) {
$(block).addClass("py").addClass("python");
hljs.highlightBlock(block);
});
// Overwrite image method to append proper prefix to the source URL
var renderer = new marked.Renderer();
var context = '{{.RawFileLink}}';
context = context.substring(0, context.lastIndexOf("/"));
renderer.image = function (href, title, text) {
return `<img src="${context}/${href}"`
};
$("#ipython-notebook .nb-markdown-cell").each(function(i, markdown) {
$(markdown).html(marked($(markdown).html(), {renderer: renderer}));
});
});
});
</script>
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
c.Header().Set("Content-Security-Policy", "default-src 'none'; style-src 'unsafe-inline'; sandbox")
Steps to Reproduce
-
As the attacker, add and push/commit a
.ipynbfile containing ajavascript:link in a Markdown cell to a repository.-
Example (PoC):
{ "nbformat": 4, "nbformat_minor": 2, "metadata": {}, "cells": [ { "cell_type": "markdown", "metadata": {}, "source": [ "[poc](javascript:alert(document.domain))" ] } ] }
-
-
The victim opens the file on Gogs (e.g.,
/<user>/<repo>/src/<branch>/poc.ipynb). <img width="2386" height="1218" alt="image" src="https://github.com/user-attachments/assets/b0d93fd8-c5ca-4058-8af0-98dee590d3ad" /> -
When the victim clicks the
poclink displayed in the preview,alert(document.domain)is executed in the same Gogs origin. <img width="2390" height="1388" alt="image" src="https://github.com/user-attachments/assets/0eb6ebe8-632c-4a41-8a11-46471514b4c4" />
Minimum Required Privileges
-
Attacker: Ability to place a
.ipynbfile 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.
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