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Fencer Vulns
high 7.6

CVE-2021-29460 json

Cross-site scripting (XSS) from unsanitized uploaded SVG files

published 2021-04-27 5 y ago modified 2026-07-08 4 mo ago also GHSA-qgp4-5qx6-548g , EUVD-2021-0862

cvss
7.6
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
3.2%
EPSS 3.2% chance of exploitation in 30 days, percentile 88%
public exploits
1
Exploit-DB

Summary

Kirby is an open source CMS. An editor with write access to the Kirby Panel can upload an SVG file that contains harmful content like `<script>` tags. The direct link to that file can be sent to other users or visitors of the site. If the victim opens that link in a browser where they are logged in to Kirby, the script will run and can for example trigger requests to Kirby's API with the permissions of the victim. This vulnerability is critical if you might have potential attackers in your group of authenticated Panel users, as they can escalate their privileges if they get access to the Panel session of an admin user. Depending on your site, other JavaScript-powered attacks are possible. Visitors without Panel access can only use this attack vector if your site allows SVG file uploads in frontend forms and you don't already sanitize uploaded SVG files. The problem has been patched in Kirby 3.5.4. Please update to this or a later version to fix the vulnerability. Frontend upload forms need to be patched separately depending on how they store the uploaded file(s). If you use `File::create()`, you are protected by updating to 3.5.4+. As a work around you can disable the upload of SVG files in your file blueprints.

Patch / fix

  • packagist getkirby/cms 3.5.4
  • getkirby kirby 3.5.4

Timeline

  1. Published
  2. First public exploit (EDB-49808)

Exploit prediction

3.17% chance of exploitation in the next 30 days, higher than 88% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • EDB-49808 Kirby CMS 3.5.3.1 - 'file' Cross-Site Scripting (XSS) webapps, 2021-04-28
  • github.com https://github.com/getkirby/kirby/security/advisories/GHSA-qgp4-5qx6-548g referenced PoC, tagged "exploit" by a source, unverified
  • packetstormsecurity.com http://packetstormsecurity.com/files/162359/Kirby-CMS-3.5.3.1-Cross-Site-Scripting.html referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 7.6 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:L/A:N
NVD 3.1 5.4 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
NVD 2.0 3.5 AV:N/AC:M/Au:S/C:N/I:P/A:N
GitHub 3.1 7.6 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:L/A:N

Affected packages

ecosystem package affected fixed in
packagist getkirby/cms
<3.5.4
3.5.4

Affected products

  • getkirby kirby

Classification

Weakness
  • CWE-79 Improper Neutralization of Input During Web Page Generation

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.