high

CVE-2026-52798

Go · gogs.io/gogs

Summary

Gogs has Stored XSS in `.ipynb` Preview

Severity
high
CVSS
8.9
EPSS
0.4% (p36)
CWE
CWE-79
Also known as
GHSA-jq8v-rmf6-65jw
Published
2026-06-22
Updated
2026-06-22

Advisory details

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

  1. As the attacker, add and push/commit a .ipynb file containing a javascript: 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))"
      ]
    }
  ]
}

  2. The victim opens the file on Gogs (e.g., /<user>/<repo>/src/<branch>/poc.ipynb).

image
  1. When the victim clicks the poc link displayed in the preview, alert(document.domain) is executed in the same Gogs origin.
image

Minimum Required Privileges

Impact

References

Related advisories

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Sources: CISA KEV (public domain), OSV.dev & GitHub Advisory Database (CC-BY-4.0), FIRST EPSS, NVD/CWE (public domain). Served live from the Stateward advisory database.