# CVE-2026-21855: Tarkov Data Manager has Unauthenticated Reflected XSS

> Attackers can execute arbitrary JavaScript in victims' browsers via malicious URLs in the Tarkov Data Manager toast notification system.

- **Severity:** Critical 9.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 7 Jan 2026
- **Updated:** 7 Jan 2026

## What is CVE-2026-21855?

CVE-2026-21855 is a critical cross-site scripting vulnerability in the-hideout tarkov-data-manager, published on 7 Jan 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

The Tarkov Data Manager is a tool to manage the Tarkov item data. Prior to 02 January 2025, a reflected Cross Site Scripting (XSS) vulnerability in the toast notification system allows any attacker to execute arbitrary JavaScript in the context of a victim's browser session by crafting a malicious URL. A series of fix commits on 02 January 2025 fixed this and other vulnerabilities.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2026-21855?

It affects 1 product.


Products: Tarkov Tarkov Data Manager.

## How do I fix CVE-2026-21855?

No fix has been published for CVE-2026-21855 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-21855 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-21855 exists.

## Other vulnerabilities in the-hideout tarkov-data-manager

- [CVE-2026-21854](https://insights.sbomify.com/CVE-2026-21854/): Tarkov Data Manager Authentication Bypass vulnerability (critical 9.8)
- [CVE-2026-21856](https://insights.sbomify.com/CVE-2026-21856/): Tarkov Data Manager has Authenticated SQL Injection (high 7.2)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-21855 and fix it if it is affected.

What it is: CVE-2026-21855 is a critical cross-site scripting vulnerability in the-hideout tarkov-data-manager, published on 7 Jan 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-21855 exists.

Affected product: the-hideout tarkov-data-manager. 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-2026-21855/ (Markdown: https://insights.sbomify.com/CVE-2026-21855/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-21855
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-21855
- OSV: https://osv.dev/vulnerability/CVE-2026-21855

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-21855/
Summaries are generated and may contain mistakes; the official description above is the record.