# CVE-2026-21866: Dify - Stored XSS in chat

> Attackers can execute arbitrary scripts in user browsers via stored XSS in chat Mermaid diagrams, affecting Dify platform users.

- **Severity:** Medium 5.1 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 3 Mar 2026
- **Updated:** 4 Mar 2026
- **Also known as:** GHSA-qpv6-75c2-75h4

## What is CVE-2026-21866?

CVE-2026-21866 is a medium-severity cross-site scripting vulnerability in langgenius dify, published on 3 Mar 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

Dify is an open-source LLM app development platform. Prior to 1.11.2, Dify is vulnerable to a stored XSS issue when rendering Mermaid diagrams within chats. This occurs because Dify’s default Mermaid configuration uses securityLevel: loose, which allows potentially unsafe content to execute. This vulnerability is fixed in 1.11.2.

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

## Which versions are affected by CVE-2026-21866?

It affects 1 product.


Products: Dify Dify.

## How do I fix CVE-2026-21866?

No fix has been published for CVE-2026-21866 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-21866 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-21866 exists.

## Other vulnerabilities in langgenius dify

- [CVE-2026-41947](https://insights.sbomify.com/CVE-2026-41947/): Dify < 1.14.2 Authorization Bypass via Trace Configuration Endpoints (critical 9.3)
- [CVE-2026-41948](https://insights.sbomify.com/CVE-2026-41948/): Dify v1.14.1 Path Traversal via Plugin Daemon Internal API Access (critical 9.3)
- [CVE-2025-0185](https://insights.sbomify.com/CVE-2025-0185/): Pandas Query Injection in langgenius/dify (high 8.8)
- [CVE-2026-61461](https://insights.sbomify.com/CVE-2026-61461/): Dify < 1.16.0-rc1 SQL Injection via MyScale Vector Store search_by_full_text (high 8.7)
- [CVE-2025-67732](https://insights.sbomify.com/CVE-2025-67732/): Dify Vulnerable to Plaintext API Key Exposure via Model Provider Configuration Endpoint (high 8.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-21866 and fix it if it is affected.

What it is: CVE-2026-21866 is a medium-severity cross-site scripting vulnerability in langgenius dify, published on 3 Mar 2026. Any signed-in user can exploit it over the network, 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-2026-21866 exists.

Affected product: langgenius dify. 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-2026-21866/ (Markdown: https://insights.sbomify.com/CVE-2026-21866/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-21866
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-21866
- OSV: https://osv.dev/vulnerability/CVE-2026-21866

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-21866/
Summaries are generated and may contain mistakes; the official description above is the record.