# 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.

- **Severity:** Medium 5.8 (`CVSS:3.1/AV:L/AC:L/PR:H/UI:R/S:U/C:H/I:H/A:N`)
- **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 available:** No
- **Published:** 17 Jun 2026
- **Updated:** 18 Jun 2026
- **Also known as:** DEBIAN-CVE-2026-48821, GHSA-mw63-f9qj-c5h3, UBUNTU-CVE-2026-48821

## 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 (Improper Neutralization of Input During Web Page Generation)

## 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.

## Is CVE-2026-48821 being exploited?

There is no known exploitation of CVE-2026-48821 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-48821 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-48821 in the wild and no public exploit code.

Affected product: Shaarli. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-48821/ (Markdown: https://insights.sbomify.com/CVE-2026-48821/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-48821
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-48821
- OSV: https://osv.dev/vulnerability/CVE-2026-48821

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-48821/
Summaries are generated and may contain mistakes; the official description above is the record.