CVE-2026-48821 Shaarli: DOM-based Cross-Site Scripting (XSS) in Thumbnail Synchronizer
An administrator running the thumbnail synchronizer can trigger DOM-based XSS via malicious bookmark titles, leading to session hijacking and privilege escalation.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-48821?
CVE-2026-48821 is a medium-severity cross-site scripting vulnerability in Shaarli, published on 17 Jun 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Official description
Shaarli is a personal bookmarking service. Versions 0.16.1 and prior contain a DOM-based Cross-Site Scripting (XSS) vulnerability in the Thumbnail Synchronizer feature. When an administrator runs the thumbnail update process, malicious bookmark titles are returned via an AJAX response and inserted into the DOM using innerHTML without proper sanitization. The issue originates from the interaction between the backend thumbnail update endpoint and the frontend JavaScript responsible for rendering update progress. On the backend, the ThumbnailsController::ajaxUpdate method returns bookmark data formatted using the 'raw' formatter. This includes the unescaped bookmark title in the JSON response. On the client side, the script thumbnails-update.js processes this AJAX response and dynamically updates the progress interface. Administrators using the thumbnail synchronization feature are affected and exploitation could lead to session hijacking, privilege escalation, backdoor injection and full compromise. This issue has been fixed in version 0.16.2.
Weakness: CWE-79
Which versions are affected by CVE-2026-48821?
How do I fix CVE-2026-48821?
No fix has been published for CVE-2026-48821 yet. Limit exposure of the affected software until one is available.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-48821 being exploited?
There is no known exploitation of CVE-2026-48821 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-48821, GHSA-mw63-f9qj-c5h3, UBUNTU-CVE-2026-48821.